We have compared two groups (n = 22) of unpremedicated patients to determine if the pain caused by injection of propofol could be modified by alfentanil. in group I, alfentanil 1 mg was given as a bolus iv. injection 15 s before administration of propofol iv., while group II received saline. Propofol was given in 20-mg increments every 4 s. All injections were given through the same i v. cannula on the dorsum of one hand. We found that alfentanil pretreatment reduced pain on injection of propofol (P = 0.001).