Twenty patients who had evidence of myoglobinuria were treated with intravenous infusions of mannitol and sodium bicarbonate. Nine patients (group 1) responded with higher urine output, and continued infusion improved renal function; none required dialysis and all survived. Eleven patients (group 2) did not respond to the infusion, and required an average of 5.3 (range, 0 to 11) dialyses; one patient died. There was no significant difference in initial BUN level, creatinine level, BUN/creatinine ratio, or fractional sodium excretion level between the two groups. However, group 2 patients had a significantly higher creatine phosphokinase (CPK) level, serum phosphate level, and hematocrit reading initially than did group 1, indicative of more severe muscle injury and hemoconcentration. These results demonstrate that some patients with myoglobinuria will respond to infusion of mannitol and sodium bicarbonate. This treatment may be effective in altering the clinical course of myoglobinuric acute renal failure.