The fine structure of right sciatic nerves of Swiss white mice was studied after being exposed to a venom solution ofAgkistrodon contortrix laticinctus (broad-banded copperhead) and to 0.9% NaCl solutions for periods of 1, 2 or 3 h. There was some “Wallerian-like” degeneration in all groups of nerves in the experiment. Additional neuropathological changes were noted in the nerves exposed to venom solutions. The connective tissue was affected most severely, while the basal lamina was unaffected. Schwann cells were vacuolated, and in the most extreme case, a type of myelin splitting occurred which was considered as a “demyelinative” effect. The results were compared to those of Martin and Rosenberg (1968) [15] on studies of the giant squid axon. References to additional fine structural studies of various other neuropathies were given.