diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,8 @@
 # Changelog for barbies
 
+## 1.1.1.0
+  - Add `bmapC` (Chris Penner).
+
 ## 1.1.0.0
   - Make all classes poly-kinded (#7): a barbie can now be any type 
     parameterised by a type `(k -> Type)`. In particular, a (higher-kinded)
diff --git a/barbies.cabal b/barbies.cabal
--- a/barbies.cabal
+++ b/barbies.cabal
@@ -1,5 +1,5 @@
 name:           barbies
-version:        1.1.0.0
+version:        1.1.1.0
 synopsis:       Classes for working with types that can change clothes.
 description:    Types that are parametric on a functor are like Barbies that have an outfit for each role. This package provides the basic abstractions to work with them comfortably.
 category:       Data-structures
diff --git a/src/Data/Barbie.hs b/src/Data/Barbie.hs
--- a/src/Data/Barbie.hs
+++ b/src/Data/Barbie.hs
@@ -80,6 +80,8 @@
     -- * Constraints and instance dictionaries
   , ConstraintsB(AllB, baddDicts)
   , AllBF
+    -- ** Utility functions
+  , bmapC
 
     -- * Products and constaints
   , ProductBC(bdicts)
@@ -106,7 +108,7 @@
 
 where
 
-import Data.Barbie.Internal.Constraints(ConstraintsB(..), AllBF)
+import Data.Barbie.Internal.Constraints(ConstraintsB(..), AllBF, bmapC)
 import qualified Data.Barbie.Internal.Constraints as Deprecated
 
 import Data.Barbie.Internal.Functor(FunctorB(..))
diff --git a/src/Data/Barbie/Constraints.hs b/src/Data/Barbie/Constraints.hs
--- a/src/Data/Barbie/Constraints.hs
+++ b/src/Data/Barbie/Constraints.hs
@@ -30,6 +30,7 @@
     -- * Retrieving dictionaries
   , ConstraintsB(..)
   , ProductBC(..)
+  , bmapC
 
   , AllBF
   , ClassF
diff --git a/src/Data/Barbie/Internal/Constraints.hs b/src/Data/Barbie/Internal/Constraints.hs
--- a/src/Data/Barbie/Internal/Constraints.hs
+++ b/src/Data/Barbie/Internal/Constraints.hs
@@ -4,6 +4,7 @@
 {-# LANGUAGE UndecidableInstances #-}
 module Data.Barbie.Internal.Constraints
   ( ConstraintsB(..)
+  , bmapC
   , AllBF
 
   , CanDeriveConstraintsB
@@ -20,7 +21,7 @@
 
 where
 
-import Data.Barbie.Internal.Dicts   (ClassF, Dict (..))
+import Data.Barbie.Internal.Dicts   (ClassF, Dict (..), requiringDict)
 import Data.Barbie.Internal.Functor (FunctorB (..))
 
 import Data.Functor.Compose (Compose (..))
@@ -85,6 +86,29 @@
        )
     => b f -> b (Dict c `Product` f)
   baddDicts = gbaddDictsDefault
+
+
+-- | Like 'bmap' but a constraint is allowed to be required on
+--   each element of @b@
+--
+-- E.g. If all fields of 'b' are 'Show'able then you 
+-- could store each shown value in it's slot using 'Const':
+--
+-- > showFields :: (AllB Show b, ConstraintsB b) => b Identity -> b (Const String)
+-- > showFields = bmapC @Show showField
+-- >   where
+-- >     showField :: forall a. Show a => Identity a -> Const String a
+-- >     showField (Identity a) = Const (show a)
+bmapC :: forall c b f g.
+      (AllB c b, ConstraintsB b)
+      => (forall a. c a => f a -> g a)
+      -> b f
+      -> b g
+bmapC f bf = bmap go (baddDicts bf)
+  where
+    go :: forall a. (Dict c `Product` f) a -> g a
+    go (d `Pair` fa) = requiringDict (f fa) d
+
 
 -- | Similar to 'AllB' but will put the functor argument @f@
 --   between the constraint @c@ and the type @a@. For example:
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -11,9 +11,10 @@
 import Barbies
 import BarbiesW
 
-import Data.Barbie (bfoldMap)
+import Data.Barbie (bfoldMap, bmapC, buniqC)
 import Data.Barbie.Bare(Covered)
 import Data.Functor.Const(Const(..))
+import Data.Functor.Identity(Identity(..))
 
 main :: IO ()
 main
@@ -181,4 +182,17 @@
                 let b = Record3 (Const "tic") (Const "tac") (Const "toe")
                 bfoldMap getConst b @?= "tictactoe"
             ]
+        , testGroup
+          "bmapC"
+          [ testCase "Record1" $
+                bmapC @Num (fmap (+1)) (Record1 (Identity 0))
+                    @?= Record1 (Identity 1)
+          ]
+        , testGroup
+          "buniqC"
+          [ testCase "Record1" $
+                buniqC @Num (Identity (fromIntegral (42 :: Int)))
+                    @?= Record1 (Identity 42)
+          ]
         ]
+