Vincristine (VCR) administration to rabbits resulted in severe electrophysiologic alterations of peripheral nerves. Sciatic nerve conduction velocity, compound action potential (CAP) amplitude, and area under the CAP waveform were all reduced in a dose-dependent fashion. In addition, the pattern of conduction velocity of both motor and sensory fibers was altered and shifted toward slow conduction classes. Simultaneous treatment with gangliosides limited significantly the changes in electrophysiologic parameters induced by VCR. It is suggested that gangliosides be given in the clinical setting as protection for the peripheral nerves against the side effects of antiblastic therapy.