The mode of action of curare, a well-known competitive antagonist of acetylcholine at the nicotinic receptor, was examined with the single channel recording technique. Curare can open cholinergic channels in rat myotubes, as suggested by Ziskind and Dennis (1978). Moreover another curare molecule can then block the curare-activated open channel, in line with previous results concerning such a mode of action. In adult rat muscle, the partial agonist activity of curare can also be demonstrated, though it is much weaker than in embryonic muscle. It is also shown that in adult muscle cell, the conductance of the channel (activated either by ACh or by curare) is 50-60 pS, i.e., higher than in the myotubes (35 pS).