The effects of various subcutaneous doses (30, 100 and 300 micrograms/kg) of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a serotonin (5-HT)1A receptor agonist, were studied on the performance of rats in a one-trial passive avoidance task. When administered 30 min before the training trial and the retention test, 8-OH-DPAT significantly reduced retention latencies at all doses. Similar results were obtained when 8-OH-DPAT was administered before either the training trial or the retention test. When administered 5 min after the training trial, 100 and 300 micrograms/kg 8-OH-DPAT significantly reduced the retention latencies whereas 30 micrograms/kg caused a non-significant tendency to a reduction. A dose of 300 micrograms/kg 8-OH-DPAT significantly raised the thresholds for various responses (flinch, jump and vocalization) elicited by electric shock applied to the grid floor while 30 and 100 micrograms/kg had no effect. When administered 30 min before the retention test to rats that could choose between a punished and unpunished compartment, 8-OH-DPAT at 100 and 300 micrograms/kg facilitated re-entry to either compartment but, like control animals, most 8-OH-DPAT-treated animals preferred the unpunished compartment. Although the effects of 8-OH-DPAT on pain perception, general activity or emotional behavior may interfere with the performance of rats in the passive avoidance task, the results suggest that at 100 and 300 micrograms/kg 8-OH-DPAT interferes with mechanisms related to the acquisition and consolidation of memory.