The effect of caffeine on neuroendocrine stress responses in the workplace was studied in 14 habitual coffee drinkers. Urinary catecholamine and cortisol levels were measured on 2 study days, in a 4-hour interval from morning until noon, while participants performed their normal work-related activities. Caffeine (300 mg) or placebo was administered blind at the beginning of study intervals, after overnight caffeine abstinence. Retrospective mood and symptom ratings were collected at the end of each morning. Caffeine elevated urinary epinephrine levels during work by 37% but did not affect norepinephrine or cortisol levels. Subjective reports suggest that caffeine abstinence was associated with symptoms of caffeine withdrawal by the end of the morning. Effects included higher ratings of sleepiness, lethargy, and headache and a reduced desire to socialize. Results suggest caffeine may increase the activity of the sympathetic adrenal-medullary system during everyday activities in the work environment. This action may potentiate psychophysiological responses elicited by occupational stressors.