Trimethyltin is a neurotoxic organometal which produces neuronal damage in several limbic regions including the hippocampus, amygdala and the pyriform cortex. One administration of trimethyltin (5,6 or 7 mg/kg) twenty one days prior to passive avoidance conditioning produced an impairment of retention when animals were tested 24 hours after training. Rats treated with trimethyltin exhibited shorter step-through latencies and freezing durations during the retention test. It was observed that the three dosages of trimethyltin were equally effective in disrupting retention performance. These retention deficits were not secondary to alterations in footshock sensitivity. The data presented here indicate that acute trimethyltin administration disrupted learning and memory. This compound might be a useful tool for examining the role of the limbic system in associative processes.