Windows Phone 8 - No serialization?

I'm getting errors when trying to build for Windows 8 & WP8 regarding serialization

 "The type or namespace name 'ISerializable" could not be found..."
 
 "The type or namespace name 'Formatters" could not be found.."
 
 "The type or namespace name 'SerializationInfo" could not be found..."

Is this not supported in Unity Windows/Phone 8 or is something wrong?