This investigation sought to characterize the interaction between GABA/benzodiazepine and opioid systems in memory retrieval deficit induced by detaining an animal in the training apparatus after acquisition. Mice pretreated with saline or Leu-enkephalin (0.2 mg/kg) were trained in one-trial passive avoidance test with following detention. Pre-testing administration of bicuculline (1 mg/kg), picrotoxin (1 mg/kg), or flumazenil (10 mg/kg) produced the memory-enhancing effect in the saline-pretreated mice. Pretraining treatment with Leu-enkephalin blocked the reactivation of memory produced by bicuculline and picrotoxin, but not flumazenil. The present investigation suggest that both benzodiazepine/GABA and opioid systems are important modulators of memory retrieval and that a specific interaction between these systems is responsible for the observed recovery of impaired memory trace.