The etiology and clinical course of acute nontraumatic rhabdomyolysis and ensuing renal failure was surveyed in a series of 40 consecutive patients. In 28 cases the muscle damage occurred after excessive consumption of ethyl alcohol and/or other intoxications. Prolonged lying immobilized was the reason or contributing factor for rhabdomyolysis in 22 cases. The other evident etiologies were convulsions, vigorous physical exercise, arterial occlusion and hypothermia. Typical local signs of rhabdomyolysis--pain, swelling and weakness of the affected muscles--were absent in one fourth of the patients. In these cases the diagnosis was based on transient elevation of serum creatine kinase enzyme activity. Dialyses were required to manage acute renal failure in 24 subjects. All 36 survivors recovered normal renal function. Neurological defects in the extremities still persisted in 16 patients at three months' follow-up.