Three groups each of 24 patients who had undergone total abdominal hysterectomy were studied on the 1st day after operation. Under double-blind conditions, group 1 compared meptazinol 60 mg with pethidine 100 mg, group 2, meptazinol 75 mg with pethidine 100 mg and group 3, meptazinol 100 mg with pethidine 100 mg. The drugs were given i.m. Analgesic activity was assessed by patients rating their pain before and 1 h after the administration of each treatment and by patient and investigator preference for treatment. From the pain relief score, pethidine was not significantly better than any dose of meptazinol in relieving pain. Patients preferred pethidine 100 mg to meptazinol 60 mg (P less than 0.01, McNemar's test), but there was no significant difference between meptazinol and pethidine for observer or patient preference when the dose of meptazinol was increased to 75 mg or 100 mg.