Propofol is increasingly being used in medical and surgical procedures in which conscious sedation of the patient is desired. The mood-altering and psychomotor effects of subanesthetic concentrations of propofol have not been well characterized. Therefore, we examined the effects of intravenous infusions of different subanesthetic doses of propofol on mood and psychomotor/cognitive performance in healthy volunteers (n = 10). A prospective, randomized, placebo-controlled, double-blind, crossover design was used in which subjects first were administered an intravenous loading dose of propofol or placebo (Intralipid) and then were infused over a 20-min period with a given dose of propofol or placebo. Each subject received placebo (Intralipid loading dose and infusion), low-dose propofol (0.08 mg/kg loading dose and 0.5 mg.kg-1.h-1 infusion), moderate-dose propofol (0.16 mg/kg loading dose and 1.0 mg.kg-1.h-1 infusion), and high-dose propofol (0.32 mg/kg loading dose and 2.0 mg.kg-1.h-1 infusion) in four sessions spaced approximately 1 week apart. Propofol induced changes in mood in a dose-related fashion. Some of these mood-altering effects lingered for as long as 30 min after termination of the infusion, but, in general mood had returned to baseline levels 1 h after termination of the infusion. Intralipid induced no changes in mood during the infusion period. Psychomotor functioning was impaired during, and anterograde amnesia was present after, the high-dose propofol infusion. These results suggest that propofol as a sedative has a spectrum of effects that are well-suited for ambulatory surgery (e.g., sedation, amnesia, and rapid and complete recovery).