The subjects were stratified into three age groups (19-40, 41-64, and > 65 yr), and each group included 10 male and 10 female volunteers. Each subject received both propofol formulations in a crossover fashion separated by a 7-day washout period, and the order of the drug administration was randomized. Subjects received both propofol formulations during 60 min. The infusion rate was assigned according to a nonblinded, randomized design to 1.5, 3, 6, or 12 mg/kg/hr.