The present study investigated the effects of caffeine on memory for supraspan word lists. Twelve groups of male and female college students classified as high or low impulsive were administered (PO) 0 mg/kg, 2 mg/kg or 4 mg/kg of caffeine. Subjects listened to four word lists presented at a fast rate and four at a slow rate. Caffeine inhibited females' recall during the slow rate, but not the fast rate. Caffeine had no effect on the recall performance of males. The observed effects of caffeine were not influenced by subjects' typical amount of caffeine consumption, verbal ability, or level of impulsivity. The results suggest that caffeine may impair the efficiency with which females rehearse information in working memory.