The purpose of the study was to compare the clinical activity of remifentanil or alfentanil. under propofol sedation with regard to respiratory rate, sedation and recovery rate when used for outpatient endometrial. biopsy. Patients were randomized to receive intravenously either bolus remifentanil 0.4 mug/kg and propofol 1 mg/kg in the remifentanil group (n = 30), or bolus alfentanil 20 mug/kg and propofol 1 mg/kg in the alfentanil group (n = 30). Patients were monitored for heart rate, systolic and diastolic arterial pressure, peripheral O-2 saturation (SpO(2)), respiration rate, and Aldrete sedation score. Pulse oximetry was used to monitor heart rate and SpO(2) during endometrial biopsy. Apnoea was observed in five patients from the remifentanil group, and in three patients from the alfentanil group. The groups did not differ with regard to apnoea incidences. Times were recorded for orientation and Aldrete score > 8, and were similar between the two groups (13.20 +/- 3.64 min and 14.0 +/- 3.87 min in the remifentanil. group, 14.7 +/- 3.64 min and 15.9 +/- 3.15 min in the alfentanil group, respectively). The sedative and analgesic combination of remifentanil-propofol does not offer any advantages compared with a combination of alfentanil-propofol with regards to respiration and recovery during sedation for outpatient endometrial biopsy.