Abstract A system from the frog has been used in vitro to study the effect of various nerve blocking agents on fast axonal transport of [ 3H]leucine-labeled proteins in the sciatic nerve. Local anesthetics of the procaine type (procaine, lidocaine and tetracaine), in contrast with tetrodotoxin (TTX), arrested the transport. The inhibition, which was a slowly appearing process, was obtained at concentrations higher than necessary to block impulse conduction. Ouabain inhibited the transport, whereas depolarization with potassium had no significant effect. In the light of these observations the possibility of interactions between ionic membrane processes and fast axonal transport is discussed.