Posttraining administration of the L-enantiomer of the competitive inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester (L-NAME, 3-100 mg/kg, ip), impaired 48-h retention of a one-trial step-through inhibitory shock-avoidance task in male Swiss mice. The effects were dose-dependent and were not observed when the D-enantiomer (D-NAME, 3-100 mg/kg, ip) was injected instead of L-NAME. Retention latencies of mice that had not received a footshock during training were not affected by L-NAME. The memory impairment produced by L-NAME was time-dependent, suggesting an action on memory storage. The effects of L-NAME on memory were overcome by the injection of L-(but not D-)arginine (300 mg/kg, ip) along with the inhibitor. Considered together, these findings suggest that the L-arginine/nitric oxide pathway may be involved in memory storage of an inhibitory avoidance response in mice.