diff --git a/lib/mongo/connection.rb b/lib/mongo/connection.rb
index e84b7ba..8da2b00 100644
--- a/lib/mongo/connection.rb
+++ b/lib/mongo/connection.rb
@@ -35,7 +35,7 @@ module Mongo
     STANDARD_HEADER_SIZE = 16
     RESPONSE_HEADER_SIZE = 20
 
-    attr_reader :logger, :size, :auths, :primary, :safe, :primary_pool, :host_to_try
+    attr_reader :logger, :size, :auths, :primary, :safe, :primary_pool, :host_to_try, :pool_size
 
     # Counter for generating unique request ids.
     @@current_request_id = 0
@@ -188,10 +188,11 @@ module Mongo
     #
     # @raise [AuthenticationError] raises an exception if any one
     #   authentication fails.
-    def apply_saved_authentication
+    def apply_saved_authentication(opts={})
       return false if @auths.empty?
       @auths.each do |auth|
-        self[auth['db_name']].authenticate(auth['username'], auth['password'], false)
+        self[auth['db_name']].issue_authentication(auth['username'], auth['password'], false,
+          :socket => opts[:socket])
       end
       true
     end
@@ -241,6 +242,14 @@ module Mongo
       true
     end
 
+    def authenticate_pools
+      @primary_pool.authenticate_existing
+    end
+
+    def logout_pools(db)
+      @primary_pool.logout_existing(db)
+    end
+
     # Return a hash with all database names
     # and their respective sizes on disk.
     #
@@ -411,7 +420,13 @@ module Mongo
       request_id = add_message_headers(message, operation)
       packed_message = message.to_s
       begin
-        sock = socket || (command ? checkout_writer : checkout_reader)
+        if socket
+          sock = socket
+          checkin = false
+        else
+          sock = (command ? checkout_writer : checkout_reader)
+          checkin = true
+        end
 
         result = ''
         @safe_mutexes[sock].synchronize do
@@ -419,7 +434,9 @@ module Mongo
           result = receive(sock, request_id)
         end
       ensure
-        command ? checkin_writer(sock) : checkin_reader(sock)
+        if checkin
+          command ? checkin_writer(sock) : checkin_reader(sock)
+        end
       end
       result
     end
@@ -588,7 +605,7 @@ module Mongo
         socket = TCPSocket.new(host, port)
         socket.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
 
-        config = self['admin'].command({:ismaster => 1}, :sock => socket)
+        config = self['admin'].command({:ismaster => 1}, :socket => socket)
       rescue OperationFailure, SocketError, SystemCallError, IOError => ex
         close
       ensure
@@ -598,16 +615,13 @@ module Mongo
       config
     end
 
-    # Set the specified node as primary, and
-    # apply any saved authentication credentials.
+    # Set the specified node as primary.
     def set_primary(node)
       host, port = *node
       @primary = [host, port]
       @primary_pool = Pool.new(self, host, port, :size => @pool_size, :timeout => @timeout)
-      apply_saved_authentication
     end
 
-
     ## Low-level connection methods.
 
     def receive(sock, expected_response)
diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index 325f565..c43fb4c 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -92,7 +92,8 @@ module Mongo
     # @param [String] password
     # @param [Boolean] save_auth
     #   Save this authentication to the connection object using Connection#add_auth. This
-    #   will ensure that the authentication will be applied on database reconnect.
+    #   will ensure that the authentication will be applied on database reconnect. Note
+    #   that this value must be true when using connection pooling.
     #
     # @return [Boolean]
     #
@@ -100,8 +101,19 @@ module Mongo
     #
     # @core authenticate authenticate-instance_method
     def authenticate(username, password, save_auth=true)
-      doc = command({:getnonce => 1}, :check_response => false)
-      raise "error retrieving nonce: #{doc}" unless ok?(doc)
+      if @connection.pool_size > 1
+        if !save_auth
+          raise MongoArgumentError, "If using connection pooling, :save_auth must be set to true."
+        end
+        @connection.authenticate_pools
+      end
+
+      issue_authentication(username, password, save_auth)
+    end
+
+    def issue_authentication(username, password, save_auth=true, opts={})
+      doc = command({:getnonce => 1}, :check_response => false, :socket => opts[:socket])
+      raise MongoDBError, "Error retrieving nonce: #{doc}" unless ok?(doc)
       nonce = doc['nonce']
 
       auth = BSON::OrderedHash.new
@@ -109,7 +121,7 @@ module Mongo
       auth['user'] = username
       auth['nonce'] = nonce
       auth['key'] = Mongo::Support.auth_key(username, password, nonce)
-      if ok?(self.command(auth, :check_response => false))
+      if ok?(self.command(auth, :check_response => false, :socket => opts[:socket]))
         if save_auth
           @connection.add_auth(@name, username, password)
         end
@@ -121,7 +133,7 @@ module Mongo
 
     # Adds a stored Javascript function to the database which can executed  
     # server-side in map_reduce, db.eval and $where clauses.
-    # 
+    #
     # @param [String] function_name
     # @param [String] code
     #
@@ -179,14 +191,22 @@ module Mongo
     end
 
     # Deauthorizes use for this database for this connection. Also removes
-    # any saved authorization in the connection class associated with this
+    # any saved authentication in the connection class associated with this
     # database.
     #
     # @raise [MongoDBError] if logging out fails.
     #
     # @return [Boolean]
-    def logout
-      doc = command(:logout => 1)
+    def logout(opts={})
+      if @connection.pool_size > 1
+        @connection.logout_pools(@name)
+      end
+
+      issue_logout(opts)
+    end
+
+    def issue_logout(opts={})
+      doc = command({:logout => 1}, :socket => opts[:socket])
       if ok?(doc)
         @connection.remove_auth(@name)
         true
@@ -455,14 +475,14 @@ module Mongo
     #
     # @option opts [Boolean] :check_response (true) If +true+, raises an exception if the
     # command fails.
-    # @option opts [Socket] :sock a socket to use for sending the command. This is mainly for internal use.
+    # @option opts [Socket] :socket a socket to use for sending the command. This is mainly for internal use.
     #
     # @return [Hash]
     #
     # @core commands command_instance-method
     def command(selector, opts={})
       check_response = opts.fetch(:check_response, true)
-      sock           = opts[:sock]
+      socket         = opts[:socket]
       raise MongoArgumentError, "command must be given a selector" unless selector.is_a?(Hash) && !selector.empty?
       if selector.keys.length > 1 && RUBY_VERSION < '1.9' && selector.class != BSON::OrderedHash
         raise MongoArgumentError, "DB#command requires an OrderedHash when hash contains multiple keys"
@@ -470,7 +490,7 @@ module Mongo
 
       begin
         result = Cursor.new(system_command_collection,
-          :limit => -1, :selector => selector, :socket => sock).next_document
+          :limit => -1, :selector => selector, :socket => socket).next_document
       rescue OperationFailure => ex
         raise OperationFailure, "Database command '#{selector.keys.first}' failed: #{ex.message}"
       end
diff --git a/lib/mongo/repl_set_connection.rb b/lib/mongo/repl_set_connection.rb
index 4f4fa00..4203a34 100644
--- a/lib/mongo/repl_set_connection.rb
+++ b/lib/mongo/repl_set_connection.rb
@@ -167,6 +167,20 @@ module Mongo
       @read_secondary || @slave_ok
     end
 
+    def authenticate_pools
+      super
+      @secondary_pools.each do |pool|
+        pool.authenticate_existing
+      end
+    end
+
+    def logout_pools(db)
+      super
+      @secondary_pools.each do |pool|
+        pool.logout_existing(db)
+      end
+    end
+
     private
 
     def check_is_master(node)
diff --git a/lib/mongo/util/pool.rb b/lib/mongo/util/pool.rb
index f96d6c1..fbcb522 100644
--- a/lib/mongo/util/pool.rb
+++ b/lib/mongo/util/pool.rb
@@ -37,6 +37,9 @@ module Mongo
       # Condition variable for signal and wait
       @queue = ConditionVariable.new
 
+      # Operations to perform on a socket
+      @socket_ops = Hash.new { |h, k| h[k] = [] }
+
       @sockets      = []
       @checked_out  = []
     end
@@ -75,11 +78,42 @@ module Mongo
       rescue => ex
         raise ConnectionFailure, "Failed to connect socket: #{ex}"
       end
+
+      # If any saved authentications exist, we want to apply those
+      # when creating new sockets.
+      @connection.apply_saved_authentication(:socket => socket)
+
       @sockets << socket
       @checked_out << socket
       socket
     end
 
+    # If a use calls DB#authentication, and several sockets exist,
+    # then we need a way to apply the authentication on each socket.
+    # So we store the apply_authentication method, and this will be
+    # applied right before the next use of each socket.
+    def authenticate_existing
+      @connection_mutex.synchronize do
+        @sockets.each do |socket|
+          @socket_ops[socket] << Proc.new do
+            @connection.apply_saved_authentication(:socket => socket)
+          end
+        end
+      end
+    end
+
+    # Store the logout op for each existing socket to be applied before
+    # the next use of each socket.
+    def logout_existing(db)
+      @connection_mutex.synchronize do
+        @sockets.each do |socket|
+          @socket_ops[socket] << Proc.new do
+            @connection.db(db).issue_logout(:socket => socket)
+          end
+        end
+      end
+    end
+
     # Checks out the first available socket from the pool.
     #
     # This method is called exclusively from #checkout;
@@ -110,14 +144,24 @@ module Mongo
                      checkout_new_socket
                    end
 
-          return socket if socket
+          if socket
 
-          # Otherwise, wait
-          if @logger
-            @logger.warn "MONGODB Waiting for available connection; " +
-              "#{@checked_out.size} of #{@size} connections checked out."
+          # This call all procs, in order, scoped to existing sockets.
+          # At the moment, we use this to lazily authenticate and
+          # logout existing socket connections.
+          @socket_ops[socket].reject! do |op|
+            op.call
+          end
+
+            return socket
+          else
+            # Otherwise, wait
+            if @logger
+              @logger.warn "MONGODB Waiting for available connection; " +
+                "#{@checked_out.size} of #{@size} connections checked out."
+            end
+            @queue.wait(@connection_mutex)
           end
-          @queue.wait(@connection_mutex)
         end
       end
     end
diff --git a/test/auxillary/threaded_authentication_test.rb b/test/auxillary/threaded_authentication_test.rb
new file mode 100644
index 0000000..d60200a
--- /dev/null
+++ b/test/auxillary/threaded_authentication_test.rb
@@ -0,0 +1,101 @@
+$:.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
+require 'mongo'
+require 'thread'
+require 'test/unit'
+require './test/test_helper'
+
+# NOTE: This test requires bouncing the server.
+# It also requires that a user exists on the admin database.
+class AuthenticationTest < Test::Unit::TestCase
+  include Mongo
+
+  def setup
+    @conn = standard_connection(:pool_size => 10)
+    @db1 = @conn.db('mongo-ruby-test-auth1')
+    @db2 = @conn.db('mongo-ruby-test-auth2')
+    @admin = @conn.db('admin')
+  end
+
+  def teardown
+    @db1.authenticate('user1', 'secret')
+    @db2.authenticate('user2', 'secret')
+    @conn.drop_database('mongo-ruby-test-auth1')
+    @conn.drop_database('mongo-ruby-test-auth2')
+  end
+
+  def threaded_exec
+    threads = []
+
+    100.times do
+      threads << Thread.new do
+        yield
+      end
+    end
+
+    100.times do |n|
+      threads[n].join
+    end
+  end
+
+  def test_authenticate
+    @admin.authenticate('bob', 'secret')
+    @db1.add_user('user1', 'secret')
+    @db2.add_user('user2', 'secret')
+    @admin.logout
+
+    threaded_exec do
+      assert_raise Mongo::OperationFailure do
+        @db1['stuff'].insert({:a => 2}, :safe => true)
+      end
+    end
+
+    threaded_exec do
+      assert_raise Mongo::OperationFailure do
+        @db2['stuff'].insert({:a => 2}, :safe => true)
+      end
+    end
+
+    @db1.authenticate('user1', 'secret')
+    @db2.authenticate('user2', 'secret')
+
+    threaded_exec do
+      assert @db1['stuff'].insert({:a => 2}, :safe => true)
+    end
+
+    threaded_exec do
+      assert @db2['stuff'].insert({:a => 2}, :safe => true)
+    end
+
+    puts "Please bounce the server."
+    gets
+
+    # Here we reconnect.
+    begin
+      @db1['stuff'].find.to_a
+      rescue Mongo::ConnectionFailure
+    end
+
+    threaded_exec do
+      assert @db1['stuff'].insert({:a => 2}, :safe => true)
+    end
+
+    threaded_exec do
+      assert @db2['stuff'].insert({:a => 2}, :safe => true)
+    end
+
+    @db1.logout
+    threaded_exec do
+      assert_raise Mongo::OperationFailure do
+        @db1['stuff'].insert({:a => 2}, :safe => true)
+      end
+    end
+
+    @db2.logout
+    threaded_exec do
+      assert_raise Mongo::OperationFailure do
+        assert @db2['stuff'].insert({:a => 2}, :safe => true)
+      end
+    end
+  end
+
+end
diff --git a/test/unit/connection_test.rb b/test/unit/connection_test.rb
index a23977f..0491f40 100644
--- a/test/unit/connection_test.rb
+++ b/test/unit/connection_test.rb
@@ -67,7 +67,6 @@ class ConnectionTest < Test::Unit::TestCase
         admin_db = new_mock_db
         admin_db.expects(:command).returns({'ok' => 1, 'ismaster' => 1}).twice
         @conn.expects(:[]).with('admin').returns(admin_db).twice
-        @conn.expects(:apply_saved_authentication)
         @conn.connect
       end
 
diff --git a/test/unit/db_test.rb b/test/unit/db_test.rb
index 9e60102..e84086b 100644
--- a/test/unit/db_test.rb
+++ b/test/unit/db_test.rb
@@ -57,6 +57,7 @@ class DBTest < Test::Unit::TestCase
 
       should "raise an error if logging out fails" do
         @db.expects(:command).returns({})
+        @conn.expects(:pool_size).returns(1)
         assert_raise Mongo::MongoDBError do
           @db.logout
         end