A low-threshold fast inactivating K+ current (I(Alth)) was recorded in isolated land snail neurons using the two-microelectrode voltage clamp method. A nootropic drug, vinpocetine, applied to the extracellular medium at a concentration of 1-100 microM potentiated I(Alth). The potentiation consisted in a rise of its peak amplitude and an increase of the half-decay time. Vinpocetine did not cause a shift of the steady-state activation and inactivation curves along the potential axis. Dibutyryl cyclic GMP (dcGMP) also increased the peak amplitude but did not change the time of current half-decay. dcAMP did not potentiate I(Alth). The possible role of K+-current potentiation in neuronal membranes in therapy of dementia is discussed.