Three different post-operative pain relief schedules were investigated in a double blind study after total hip replacement. Group BS received a priming dose of buprenorphine i.m. at the time of wound closure and continued with sublingual buprenorphine every eight hours. Supplementary doses of buprenorphine i.m. could be demanded. Group B and M received a priming dose of buprenorphine and morphine respectively, and continued with sublingual placebo eight hourly. Supplementary doses of buprenorphine could be demanded by patients in Group B and supplementary doses of morphine by patients in Group M. On one occasion VAS scorings of groups BS and B were statistically significantly lower than group M, and on another occasion VAS scorings of group BS were statistically significantly lower than the other two groups. Furthermore, the number of on demand supplementary doses was statistically significantly higher in group M. It is concluded that buprenorphine administered at regular intervals as well as on demand provided better postoperative analgesia than morphine at present dose levels. In this context, only moderate advantages were obtained by administering buprenorphine at regular intervals.