diff --git a/lib/mongo/objectid.rb b/lib/mongo/objectid.rb
index f5f73be..cbc340c 100644
--- a/lib/mongo/objectid.rb
+++ b/lib/mongo/objectid.rb
@@ -53,6 +53,18 @@ module XGen
         @@index_time = Time.new.to_i
         @@index = 0
 
+        # Given a string representation of an ObjectID, return a new ObjectID
+        # with that value.
+        def self.from_string(str)
+          data = []
+          i = str.to_i(16)
+          while i > 0
+            data << (i & 0xff)
+            i >>= 8
+          end
+          self.new(data.reverse)
+        end
+
         # +data+ is an array of bytes. If nil, a new id will be generated.
         # The time +t+ is only used for testing; leave it nil.
         def initialize(data=nil, t=nil)
diff --git a/tests/test_objectid.rb b/tests/test_objectid.rb
index 9bc356f..86ba45f 100644
--- a/tests/test_objectid.rb
+++ b/tests/test_objectid.rb
@@ -65,4 +65,12 @@ class ObjectIDTest < Test::Unit::TestCase
     assert_equal @o, row['_id']
   end
 
+  def test_from_string
+    hex_str = @o.to_s
+    o2 = ObjectID.from_string(hex_str)
+    assert_equal hex_str, o2.to_s
+    assert_equal @o, o2
+    assert_equal @o.to_s, o2.to_s
+  end
+
 end