These experiments examined the effects of d-amphethamine on retention of one-trial inhibitory (passive) avoidance training in mice. Water-deprived mice were pretrained to lick from a water spout at the end of a darkened compartment. Footshock was administered during licking after 4, 6, or 7 days of pretraining. Retention performance (latency to lick) was measured 24 h after training. The effects on memory of posttraining amphetamine varied not only with amphetamine dose but also with the amount of pretraining. In animals pretraining for 7 days, 0.3 and 1.0 mg/kg but not 0.03, 0.1, or 3.0 mg/kg posttraining amphetamine significantly enhanced later retention performance. In mice pretrained for 6 days, 1 mg/kg amphetamine also enhanced retention performance. However, in mice pretrained for only 4 days, 1 mg/kg amphetamine impaired later retention erd for only 4 days, 1 mg/kg amphetamine impaired later retention performance. These results are consistent with the view that posttraining treatment may affect memory storage processes by interacting with training-related arousal levels.