diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,6 @@
-# 0.1.2  (April 2015)
+# 0.1.2  (May 2015)
+    * Add a 'member' convenience function
+
+# 0.1.1  (April 2015)
 	* Add 'fromList' and 'unsafeToList' functions
 	* Add basic tests
diff --git a/src/Control/Concurrent/STM/Map.hs b/src/Control/Concurrent/STM/Map.hs
--- a/src/Control/Concurrent/STM/Map.hs
+++ b/src/Control/Concurrent/STM/Map.hs
@@ -22,6 +22,7 @@
       -- * Query
     , lookup
     , phantomLookup
+    , member
 
       -- * Lists
     , fromList
@@ -90,6 +91,16 @@
 delete k m = do var <- getTVar k m
                 writeTVar var Nothing
 {-# INLINABLE delete #-}
+
+-----------------------------------------------------------------------
+
+-- |/O(log n)/. Is the key a member of the map?
+member :: (Eq k, Hashable k) => k -> Map k v -> STM Bool
+member k m = do
+    v <- lookup k m
+    case v of
+        Nothing -> return False
+        Just _  -> return True
 
 -----------------------------------------------------------------------
 
diff --git a/ttrie.cabal b/ttrie.cabal
--- a/ttrie.cabal
+++ b/ttrie.cabal
@@ -1,5 +1,5 @@
 name:                ttrie
-version:             0.1.1
+version:             0.1.2
 synopsis:            Contention-free STM hash map
 description:
   A contention-free STM hash map.