SCAssign (side-chain assignment) is a Sparky extension written in Python to assist the NMR resonance assignment of aliphatic side-chains of uniformly (13)C,(15)N-labeled large proteins. It is based on a general strategy recently developed in our laboratory that makes use of 4D (13)C,(15)N-edited NOESY, 3D MQ-(H)CC(m)H(m)-TOCSY, and prior backbone assignments. The program runs on all operating systems for which Sparky is available, and is easy to install, setup and use. Not only can it accelerate the assignment process, it also allows assignments of weak NOEs in 4D NOESY, which used to be very difficult with manual approach.