diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index 9b05c6d..409079c 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -73,9 +73,12 @@ module XGen
           @pk_factory = pk_factory
         end
 
+        # Instances of DB are normally obtained by calling Mongo#db.
+        #
         # db_name :: The database name
         #
-        # nodes :: An array of [host, port] pairs.
+        # nodes :: An array of [host, port] pairs. See Mongo#new, which offers
+        #          a more flexible way of defining nodes.
         #
         # options :: A hash of options.
         #
diff --git a/lib/mongo/mongo.rb b/lib/mongo/mongo.rb
index b1bafeb..2ff71ea 100644
--- a/lib/mongo/mongo.rb
+++ b/lib/mongo/mongo.rb
@@ -27,12 +27,16 @@ module XGen
 
         # Create a Mongo database server instance. You specify either one or a
         # pair of servers. If one, you also say if connecting to a slave is
-        # OK. The host default is "localhost" and port default is
-        # DEFAULT_PORT. If you specify a pair, pair_or_host is an array of two
-        # arrays, where each is a host/port pair (or a host with no port), and
-        # the +port+ argument is ignored.
+        # OK. In either case, the host default is "localhost" and port default
+        # is DEFAULT_PORT.
         #
-        # Options are passed on to each DB instance:
+        # If you specify a pair, pair_or_host is a hash with two keys :left
+        # and :right. Each key maps to either
+        # * a server name, in which case port is DEFAULT_PORT
+        # * a port number, in which case server is "localhost"
+        # * an array containing a server name and a port number in either order
+        #
+        # +options+ are passed on to each DB instance:
         #
         # :slave_ok :: Only used if one host is specified. If false, when
         #              connecting to that host/port a DB object will check to
@@ -51,11 +55,20 @@ module XGen
         #  Mongo.new                         # localhost, DEFAULT_PORT, !slave
         #  Mongo.new("localhost")            # localhost, DEFAULT_PORT, !slave
         #  Mongo.new("localhost", 3000)      # localhost, 3000, slave not ok
-        #  Mongo.new("localhost", 3000, :slave_ok => true) # localhost, 3000, slave ok
+        #  # localhost, 3000, slave ok
+        #  Mongo.new("localhost", 3000, :slave_ok => true)
+        #  # localhost, DEFAULT_PORT, auto reconnect
+        #  Mongo.new(nil, nil, :auto_reconnect => true)
+        #
         #  # A pair of servers. DB will always talk to the master. On socket
         #  # error or "not master" error, we will auto-reconnect to the
         #  # current master.
-        #  Mongo.new([["db1.example.com", 3000], ["db2.example.com", 3000]]], nil, :auto_reconnect => true)
+        #  Mongo.new({:left  => ["db1.example.com", 3000],
+        #             :right => "db2.example.com"}, # DEFAULT_PORT
+        #            nil, :auto_reconnect => true)
+        #
+        #  # Here, :right is localhost/DEFAULT_PORT. No auto-reconnect.
+        #  Mongo.new({:left => ["db1.example.com", 3000]})
         #
         # When a DB object first connects to a pair, it will find the master
         # instance and connect to that one.
@@ -63,8 +76,11 @@ module XGen
           @pair = case pair_or_host
                    when String
                      [[pair_or_host, port || DEFAULT_PORT]]
-                   when Array
-                     pair_or_host.collect { |nh| [nh[0], nh[1] || DEFAULT_PORT] }
+                   when Hash
+                    connections = []
+                    connections << pair_val_to_connection(pair_or_host[:left])
+                    connections << pair_val_to_connection(pair_or_host[:right])
+                    connections
                    when nil
                      [['localhost', DEFAULT_PORT]]
                    end
@@ -111,6 +127,26 @@ module XGen
 
         protected
 
+        # Turns an array containing an optional host name string and an
+        # optional port number integer into a [host, port] pair array.
+        def pair_val_to_connection(a)
+          case a
+          when nil
+            ['localhost', DEFAULT_PORT]
+          when String
+            [a, DEFAULT_PORT]
+          when Integer
+            ['localhost', a]
+          when Array
+            connection = ['localhost', DEFAULT_PORT]
+            connection[0] = a[0] if a[0].kind_of?(String)
+            connection[0] = a[1] if a[1].kind_of?(String)
+            connection[1] = a[0] if a[0].kind_of?(Integer)
+            connection[1] = a[1] if a[1].kind_of?(Integer)
+            connection
+          end
+        end
+
         # Send cmd (a hash, possibly ordered) to the admin database and return
         # the answer. Raises an error unless the return is "ok" (DB#ok?
         # returns +true+).
diff --git a/tests/test_db.rb b/tests/test_db.rb
index 70a1e90..00bdc5a 100644
--- a/tests/test_db.rb
+++ b/tests/test_db.rb
@@ -50,10 +50,10 @@ class DBTest < Test::Unit::TestCase
     assert_equal 'ruby-mongo-test.test', @db.full_coll_name(coll.name)
   end
 
-  def test_array
+  def test_pair
     @db.close
     @users = nil
-    @db = Mongo.new([["nosuch.example.com"], [@host, @port]]).db('ruby-mongo-test')
+    @db = Mongo.new({:left => "nosuch.example.com", :right => [@host, @port]}).db('ruby-mongo-test')
     assert @db.connected?
   end
 
diff --git a/tests/test_mongo.rb b/tests/test_mongo.rb
index 1e6afe7..cfce068 100644
--- a/tests/test_mongo.rb
+++ b/tests/test_mongo.rb
@@ -41,4 +41,24 @@ class MongoTest < Test::Unit::TestCase
     assert !@mongo.database_names.include?('will-be-deleted')
   end
 
+  def test_pair
+    db = Mongo.new({:left => ['foo', 123]})
+    pair = db.instance_variable_get('@pair')
+    assert_equal 2, pair.length
+    assert_equal ['foo', 123], pair[0]
+    assert_equal ['localhost', Mongo::DEFAULT_PORT], pair[1]
+
+    db = Mongo.new({:right => 'bar'})
+    pair = db.instance_variable_get('@pair')
+    assert_equal 2, pair.length
+    assert_equal ['localhost', Mongo::DEFAULT_PORT], pair[0]
+    assert_equal ['bar', Mongo::DEFAULT_PORT], pair[1]
+
+    db = Mongo.new({:right => [123, 'foo'], :left => 'bar'})
+    pair = db.instance_variable_get('@pair')
+    assert_equal 2, pair.length
+    assert_equal ['bar', Mongo::DEFAULT_PORT], pair[0]
+    assert_equal ['foo', 123], pair[1]
+  end
+
 end