The study examined the effect of pre- and post-training bilateral amygdaloid lesions on retention of a one-trial inhibitory avoidance response. Groups of rats, including unimplanted controls and implanted controls, were trained and tested for retention at 4, 7 or 12 days following training. The lesions were made at one of several intervals before or after training: 2 days before, immediately after, or 2, 5 or 10 days after. At all retention intervals the retention of implanted controls was poorer than that of unimplanted controls and, in comparison with both control groups, the retention of animals lesioned before training was impaired. Retention was also impaired by the post-training lesions. The degree of impairment varied with the interval between the training and the lesion: lesions made within 2 days following training impaired retention, while lesions made 10 days following training had no impairing effect. These findings suggest that post-training lesions of the amygdala affect retention by impairing time-dependent processes involved in memory storage. With a sufficiently long training-lesion interval (10 days) an intact amygdala is not essential for retention.