Post-training administration of the GABA-A and GABA-B receptor agonists muscimol and baclofen dose-dependently impaired retention of an inhibitory avoidance response in C57 mice, while improving memory consolidation in the DBA strain. By contrast, picrotoxin (blocker of GABA-activated ionophores), bicuculline (GABA-A antagonist) and CGP 35348 (GABA-B antagonist) dose-dependently improved retention in C57 mice and impaired it in DBA mice. These effects cannot be ascribed to non-specific actions of the drugs on retention performance, as the latencies during the retention test of those mice that had not received footshock during the training were not lengthened by the post-training drug administration. The effects on retention performance induced by GABA agonists and antagonists are probably due to an effect on memory consolidation, since they are observed when the drugs are given at short, but not at long, intervals after training. These results are discussed in terms of possible interaction of GABA systems with endogenous opioid and dopamine systems, whose activation has been shown to produce strain-dependent effects on memory processes. The possible utilization of these results for a genetic behavioral approach with recombinant inbred (RI) mice is also considered.