Caffeine withdrawal was examined in caffeine-dependent humans living in a residential laboratory. Ten men and 2 women who reported daily caffeine consumption participated in a 17-day study. From 1000-1700, participants worked on computerized tasks assessing memory, vigilance, and psychomotor skills, with a 1-hr break for lunch. From 1700-2330, participants engaged in private or social, recreational activities. Subjective-effects measures were completed 10 times per day. Participants were maintained on caffeine (100 mg 3 times a day at 0945, 1345, and 1745), except on days 5-6 and 12-13, when caffeine was replaced by placebo. Caffeine abstinence selectively influenced subjective effects without altering social behavior or performance on tasks assessing memory, vigilance, and psychomotor skills. Furthermore, the effects of caffeine on food intake were enhanced after 2 days of caffeine abstinence.