In a single-blind study of several doses of a new hexahydroazepine analgesic, meptazinol, in 45 patients recovering from major abdominal surgery, there was a dose-related significant analgesic effect from i.m. doses exceeding 50 mg. Pain relief was maximal at the end of 1 h and the duration of effect of the 100-mg dose was approximately 5 h. There was a good correlation between pain relief assessed by the patient, by the physician, and indirectly by pulmonary function tests. Heart rate and arterial pressure were not affected by meptazinol. There were no abnormal biochemical or haematological findings and the only side-effect was vomiting in a few patients receiving multiple doses of the drug.