Postoperative muscle pain occurred in 17.2% of patients given diazepam intravenously 5 minutes prior to suxamethonium. The incidence of muscle pain was 48% in those patients who were not given diazepam before suxamethonium. The difference is statistically significant (p less than 0.01). Five mg diazepam reduced the incidence of pain but not significantly (p = 0.30); 10 mg diazepam significantly reduced the incidence (p less than 0.05); while 15 and 20 mg diazepam showed better effects (p less than 0.01). Diazepam pretreatment also reduced the severity, frequency and duration of muscle pain. The incidence of fasciculations was significantly reduced but there was no correlation between the incidence of fasciculations and the occurrence of muscle pains.