diff --git a/CHANGELOG.md b/CHANGELOG.md
index b6918b29e..5b93645ec 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - #777, Empty body is allowed when calling a non-parameterized RPC - @koulakis
 - #831, Fix proc resource embedding issue with search_path - @steve-chavez
 - #857, Fix swagger-ui when "server-proxy-uri" is not set - @feynmanliang
+- #547, Use read-only transaction for stable/immutable RPC - @begriffs
 
 ## [0.4.0.0] - 2017-01-19
 
diff --git a/src/PostgREST/App.hs b/src/PostgREST/App.hs
index 73235e57c..c60335699 100644
--- a/src/PostgREST/App.hs
+++ b/src/PostgREST/App.hs
@@ -79,15 +79,29 @@ postgrest conf refDbStructure pool getTime =
             eClaims = jwtClaims jwtSecret (iJWT apiRequest) time
             authed = containsRole eClaims
             handleReq = runWithClaims conf eClaims (app dbStructure conf) apiRequest
-            txMode = transactionMode $ iAction apiRequest
+            txMode = transactionMode dbStructure
+              (iTarget apiRequest) (iAction apiRequest)
         response <- P.use pool $ HT.transaction HT.ReadCommitted txMode handleReq
         return $ either (pgError authed) identity response
     respond response
 
-transactionMode :: Action -> H.Mode
-transactionMode ActionRead = HT.Read
-transactionMode ActionInfo = HT.Read
-transactionMode _ = HT.Write
+transactionMode :: DbStructure -> Target -> Action -> H.Mode
+transactionMode structure target action =
+  case action of
+    ActionRead -> HT.Read
+    ActionInfo -> HT.Read
+    ActionInspect -> HT.Read
+    ActionInvoke ->
+      let proc =
+            case target of
+              (TargetProc qi) -> M.lookup (qiName qi) $
+                                   dbProcs structure
+              _               -> Nothing
+          v = fromMaybe Volatile $ pdVolatility <$> proc in
+      if v == Stable || v == Immutable
+         then HT.Read
+         else HT.Write
+    _ -> HT.Write
 
 app :: DbStructure -> AppConfig -> ApiRequest -> H.Transaction Response
 app dbStructure conf apiRequest =
diff --git a/src/PostgREST/DbStructure.hs b/src/PostgREST/DbStructure.hs
index 1bc2142ca..faf779f62 100644
--- a/src/PostgREST/DbStructure.hs
+++ b/src/PostgREST/DbStructure.hs
@@ -100,10 +100,19 @@ decodeSynonyms cols =
 accessibleProcs :: H.Query Schema (M.HashMap Text ProcDescription)
 accessibleProcs =
   H.statement sql (HE.value HE.text)
-    (M.fromList . map addName <$> HD.rowsList (ProcDescription <$> HD.value HD.text
-                                <*> (parseArgs <$> HD.value HD.text)
-                                <*> (parseRetType <$> HD.value HD.text <*> HD.value HD.text <*>
-                                                      HD.value HD.bool <*> HD.value HD.char))) True
+    (M.fromList . map addName <$>
+      HD.rowsList (
+        ProcDescription <$> HD.value HD.text
+                        <*> (parseArgs <$> HD.value HD.text)
+                        <*> (parseRetType <$>
+                            HD.value HD.text <*>
+                            HD.value HD.text <*>
+                            HD.value HD.bool <*>
+                            HD.value HD.char)
+                        <*> (parseVolatility <$>
+                            HD.value HD.char)
+      )
+    ) True
  where
   addName :: ProcDescription -> (Text, ProcDescription)
   addName pd = (pdName pd, pd)
@@ -124,25 +133,32 @@ accessibleProcs =
   parseRetType schema name isSetOf typ
     | isSetOf   = SetOf pgType
     | otherwise = Single pgType
-    where 
+    where
       qi = QualifiedIdentifier schema name
-      pgType = case typ of 
+      pgType = case typ of
         'c' -> Composite qi
         'p' -> Pseudo name
         _   -> Scalar qi -- 'b'ase, 'd'omain, 'e'num, 'r'ange
-          
+
+  parseVolatility :: Char -> ProcVolatility
+  parseVolatility 'i' = Immutable
+  parseVolatility 's' = Stable
+  parseVolatility 'v' = Volatile
+  parseVolatility _   = Volatile -- should not happen, but be pessimistic
+
   sql = [q|
   SELECT p.proname as "proc_name",
          pg_get_function_arguments(p.oid) as "args",
          tn.nspname as "rettype_schema",
          coalesce(comp.relname, t.typname) as "rettype_name",
          p.proretset as "rettype_is_setof",
-         t.typtype as "rettype_typ"
+         t.typtype as "rettype_typ",
+         p.provolatile
   FROM pg_proc p
     JOIN pg_namespace pn ON pn.oid = p.pronamespace
     JOIN pg_type t ON t.oid = p.prorettype
     JOIN pg_namespace tn ON tn.oid = t.typnamespace
-    LEFT JOIN pg_class comp ON comp.oid = t.typrelid 
+    LEFT JOIN pg_class comp ON comp.oid = t.typrelid
   WHERE  pn.nspname = $1|]
 
 accessibleTables :: H.Query Schema [Table]
diff --git a/src/PostgREST/Types.hs b/src/PostgREST/Types.hs
index 4895aab7e..8b760e849 100644
--- a/src/PostgREST/Types.hs
+++ b/src/PostgREST/Types.hs
@@ -41,10 +41,14 @@ data PgType = Scalar QualifiedIdentifier | Composite QualifiedIdentifier | Pseud
 
 data RetType = Single PgType | SetOf PgType deriving (Eq, Show)
 
+data ProcVolatility = Volatile | Stable | Immutable
+  deriving (Eq, Show)
+
 data ProcDescription = ProcDescription {
   pdName       :: Text
 , pdArgs       :: [PgArg]
 , pdReturnType :: RetType
+, pdVolatility :: ProcVolatility
 } deriving (Show, Eq)
 
 type Schema = Text
diff --git a/test/fixtures/schema.sql b/test/fixtures/schema.sql
index 1a19b45d4..51ec8ce62 100755
--- a/test/fixtures/schema.sql
+++ b/test/fixtures/schema.sql
@@ -316,6 +316,7 @@ $$;
 
 CREATE FUNCTION sayhello(name text) RETURNS text
     LANGUAGE sql
+    IMMUTABLE
     AS $_$
     SELECT 'Hello, ' || $1;
 $_$;