Tissue culture systems have been developed in which neuromuscular junctions form rapidly de novo. Using high-resolution Nomarski optics and electrophysiologic techniques, the development and distribution of acetylcholine receptors on the muscle surface membrane have been continuously monitored on single cells during early stages of synapse formation. A small computer has been used to detect the first signs of neuromuscular transmission. Also the role that innervation plays on the expression of different molecular forms of actetylcholinesterase has been studied.