diff --git a/README.md b/README.md
index 93ea85d..4dfc0d0 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,13 @@ Note: only the asynchronous API is supported, due to the limitations of having t
 
 ```js
 var randomBytes = require('react-native-randombytes')
+
+// synchronous API
+// uses SJCL
+var rand = randomBytes(4)
+
+// asynchronous API
+// uses iOS-side SecRandomCopyBytes
 randomBytes(4, (err, bytes) => {
   console.log(bytes.toString('hex'))
 })