Some research on the stimulant effect of caffeine suggests that the amount of behavioral enhancement produced by caffeine may depend on subjects' prior experience with the task and the drug. A study was undertaken to test whether prior experience with a task while under the influence of caffeine would facilitate performance of that task. Male (N=20) and female (N=20) college students were assigned to high or low caffeine user groups based on their self-reported caffeine consumption. Subjects received either 200 milligrams of caffeine or a placebo, orally, before completing tasks which they were likely to have performed previously while using caffeine (writing rate and reading comprehension) and which they were unlikely to have performed previously while using caffeine (tapping rate, reaction time, and serial learning). Subjects also completed the Extroversion/Introversion scale and guessed whether or not they had been given caffeine. Data analyses revealed that caffeine consumption produced no significant effects on reading comprehension, writing rate, tapping rate, reaction time, or serial recall. The drug guess test showed that subjects were not able to detect which drug they had received. A significant positive correlation was found between extroversion/introversion scores and caffeine consumption, suggesting a strong relationship between extroversion and caffeine use. (NRB)