The effects of three K+ channel blockers, 4-aminopyridine, 3,4-diaminopyridine and apamin, on scopolamine- or electroconvulsive shock-induced amnesia were investigated in mice by using a one-trial step-down passive avoidance system. Scopolamine and electroconvulsive shuck reduced the retention latency of passive avoidance, which indicated the amnestic effect of these treatments. 4-Aminopyridine, 3,4-diaminopyridine and apamin injected immediately after the acquisition trial, reversed the amnestic effect of scopolamine or electroconvulsive shuck in a dose-dependent manner. None of the drugs or electroconvulsive shock treatment affected the rotarod or activity cage performance of the mice. These results indicate that K+ channel blockers may improve cognitive deficits when memory is impaired by a drug or any other manipulation. (C) 2000 Elsevier Science B.V. All rights reserved.