Four experiments examined whether posttraining deliveries of drugs modified the performance of the rabbit's conditioned nictitating membrane response (NMR) during acquisition and extinction. The results show that ketamine accelerated, but that amphetamine, chlorpromazine, and scopolamine retarded, conditioning when the drugs were injected immediately after the completion of daily training sessions. However, all conditioning effects of the drugs were lost when their deliveries were delayed by 2 hr after the end of training. During extinction, the only drug that altered conditioned performance was ketamine. Specifically, ketamine retarded the rate of extinction when the drug was given immediately after training. However, delaying ketamine by 2 hr after training neutralized the drug's influence. These findings indicate that the NMR preparation should be useful in examining how the posttraining delivery of drugs influences associative processes in conditioning.