Proteins involved in nerve excitation and conduction were studied using a variety of biochemical approaches. The most direct approach involved the use of radioactively labeled tetrodotoxin and saxitoxin. These toxins bind specifically to proteins involved in nerve excitation and are thus a very convenient probe for studying these proteins. The involvement of lipids and fatty acids in this binding was studied and found to be important in stabilizing the binding sites. Another approach involved studying the proteins from the interior of the squid giant axons. This approach revealed the presence of a calcium-activated protease in the axoplasm of this cell. The substrate for this protease was found to be neurofilament protein, a protein that may well be involved in the process of nerve conduction. Since calcium accumulates inside an axon during excitation, this work has some profound implications regarding nerve conduction, implications which will be studied during the forthcoming year. The binding of radioactive calcium to membrane fragments isolated from crab nerve was also studied. This binding was found to be dependent on the monovalent cation species in the buffer.