This communication describes recent studies of an acetylcholine receptor from the electric ray Torpedo californica. For characterization of neurotransmitter receptors at the biochemical and biophysical levels, it is necessary to obtain at least milligram quantities of the molecules involved. Torpedo electroplax constitute an excellent source for these receptors. To understand molecular mechanisms involved in postsynaptic depolarization due to interaction of neurotransmitter with its receptor, studies can and should be conducted at several physical levels, viz. cellular, membrane, isolated molecule and reconstituted systems. Most of the work for the study of acetylcholine receptors at the cellular level has been done on vertebrate neuromuscular junctions or on Electrophorus electricus electroplax. Torpedo electroplax are not so well suited for such studies since the individual cells are basically too thin for the insertion of microelectrodes. Studies on this system can, however, be conducted at the membrane level, on isolated receptor molecules and on reconstituted systems. In this communication we describe studies at two of these levels, the membrane level and isolated receptor molecules. Several important questions can be answered by reconstitution, and this has now been achieved (Michaelson and Raftery, in press, 1974).