Studies were carried out on the effects of piracetam (4-20 mM) on the electrical activity of identified neurons in the isolated central nervous system of the pond snail in conditions of single-electrode intracellular stimulation and recording. Piracetam-induced changes were seen in 60-70% of the neurons studied. Different parameters showed different sensitivities to piracetam: the most frequent changes were in the action potential generation threshold, the slope and shape of the steady-state voltage-current characteristics of neuron membranes, and the appearance of piracetam-induced transmembrane ion currents. Nifedipine and cadmium ions, both of which are calcium channel blockers, generally reversed or weakened the effects of piracetam on the changes seen in test cells. This indicates that the effects of piracetam result from its action on calcium channels; selective changes in calcium channels may determine which piracetam-induced effects appear at the cellular level. It is hypothesized that the piracetam-sensitive cellular plasticity mechanisms may make a significant contribution to its nootropic action at the behavioral level.