In a double-blind, randomized study of 29 patients who underwent orthopedic procedures we studied the additional effect of intrathecal buprenorphine on isobaricpinal anesthesia and postoperative analgesia. The injections were 20 mg tetracaine (19 patients) or 20 mg tetracaine plus 0.15 mg buprenorphine (10 patients). In both groups the drugs were contained within a total volume of 4 ml cerebrospinal fluid. Progression and regression of the sensory blockade of spinal anesthesia were estimated with pinprick; the motor blockade was judged by the Bromage scheme. Postoperative pain was evaluated by the patients using an analogue scale after Scott and Huskisson. Arterial blood gases, respiratory rate, blood pressure, and heart rate were measured and other side-effects determined. Both groups were comparable in age, body weight, height and duration of operation (Table 1). The addition of buprenorphine elevated the sensory blockade by three segments both during spread and regression of anesthesia (Figs. 1, 2). Postoperative analgesia was better up to 8 h after injection (p less than 0.05), after 8 h pain levels were equal in test and control groups (Fig. 3). After buprenorphine patients became aware of pain sensation 13 h after injection; in the control group the pain-free interval lasted only 9 h (p greater than 0.05). There were no differences in the need for postoperative analgesics between both groups. The respiratory rate was lower during the whole period of observation (p less than 0.05). The mean values for PaCO2, pH and BE were similar in both groups (Fig. 4). PaO2 was elevated in the buprenorphine group. There was no essential alteration of blood pressure after buprenorphine. The pulse rate, however, was slightly diminished.(ABSTRACT TRUNCATED AT 250 WORDS)