Interference with dopaminergic, GABAergic or cholinergic activity of the substantia nigra is sufficient to disrupt cognitive functions. In spite of the known interactions between these neurotransmitters and serotonin, there is a notable scarcity of data germane to the participation of nigral serotonin in learning and memory. It was important, therefore, to investigate the possible involvement of serotonin in cognition. Pre-training injections of serotonin into the nigra of rats produced strong amnesia of an aversively-motivated task (inhibitory avoidance) compared to similar injections into the cerebral cortex and zona incerta. The present findings support the hypothesis that nigral serotonergic activity is involved in memory functions.