Background : Minimum alveolar concentration (MAC) is decreased during pregnancy, but there are no data regarding the requirements for intravenous agents. Recently only one study showed that the requirement for thiopental in pregnant women of 7∼13 weeks' gestation was less than the requirement obtained in nonpregnant women. Thus we wanted to determine whether pregnant patients needed less propofol for hypnosis and anesthesia than nonpregnant patients. Methods : One hundred nonpregnant women having gynecologic surgery and 100 pregnant women of 5∼13 weeks' gestation undergoing elective abortions were recruited. They were randomly allocated 10 groups according to the doses of propofol and each group had 10 patients. During a period of 30 seconds, one of the doses of propofol 1.0, 1.25, 1.5, 1.75, 2.0, 2.25, 2.5, 2.75, 3.0 or 3.25 mg/kg was administered. Two minutes later, patients were asked to open their eyes as a test for hypnosis. Patients who did not open their eyes were given a 10 seconds, 50-Hz, 80-mA transcutaneous tetanic electrical stimulus to the ulnar nerve as a test for anesthesia. Estimates of ED50 and ED95 for hypnosis and anesthesia were obtained by logistic regression. Results : In the pregnant women, the median effective doses (ED50) (95% confidence interval) for hypnosis and anesthesia were 1.25 (1.13∼1.35) mg/kg and 2.71 (2.49∼3.04) mg/kg, the ED95 (95% CI) were 1.51 (1.16∼1.87) mg/kg and 3.04 (2.80∼3.58) mg/kg respectively. Whereas in the nonpregnant women, the ED50 for hypnosis and anesthesia were 1.27 (1.39∼1.90) mg/kg and 4.12 (3.50∼6.01) mg/kg, the ED95 were 1.53 (1.41∼1.93) mg/kg and 4.35 (3.66∼7.26) mg/kg respectively. Conclusions : In early pregnant women, the doses of propofol for hypnosis and anesthesia were 1.6% and 34.2% less compared with those in nonpregnant women. (Korean J Anesthesiol 1999; 36: 93∼98)