Twenty-four patients who underwent elective cholecystectomy received double-blind increments of either pethidine 30 mg or a mixture of pethidine 30 mg and doxapram 45 mg delivered on a patient-controlled basis. A loading dose of doxapram 100 mg or saline was administered. There was no difference in respiratory depression as indicated by respiratory frequency and end tidal carbon dioxide concentration. The incidence of respiratory apnoea was similar in the two groups but apnoea was of shorter duration in patients who received doxapram, although the difference was not significant. Patients who received doxapram assessed overall pain as worse on a linear analogue scale (p less than 0.05) but demanded similar amounts of pethidine. There was no difference in pain on movement.