The effects of food deprivation on the subjective, psychomotor, and physiological responses to intravenous fentanyl (50 micrograms/70 kg) were studied in 6 healthy male volunteers. A randomized, placebo-controlled, crossover design was used in which subjects were injected with fentanyl or saline after either 2, 12, or 24 hours of fasting. Subjects completed several subjective effects questionnaires as well as psychomotor tasks prior to, and at regular intervals, following the intravenous injection for a 3-hour period. An observer-rated behavioral checklist was completed at regular intervals during the session and several physiological measures (including measurement of pupil size) were recorded. Fentanyl induced opiate-like mood changes, miosis (pupil constriction), and impairment of extraocular muscle control, and 4 of the 6 subjects reported liking the effects; however, fasting had no impact on any of fentanyl's effects. We conclude that food deprivation up to 24 hours does not alter the subjective, psychomotor, or physiological response to the opiate, fentanyl.