Research has suggested that behavioral differences may account for the effects of caffeine on information processing. To investigate the effects of caffeine on memory for supraspan word lists, 107 college students (47 males, 60 females), divided into 12 groups by high and low impulsivity scores on the Eysenck Personality Inventory, participated in the study. The subjects were administered either O, 2, or 4 milligrams of caffeine per kilogram of body weight. Following a 30-minute absorption period, subjects listened to four word lists presented at a fast rate and four word lists presented at a slow rate. Immediately after the presentation of each word list, oral recall was obtained. An analysis of the results showed that 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. These results suggest that caffeine may impair the effeciency with which females rehearse information in working memory. (Author/BL)