During two year periods between 1979 and 1981, we have experienced 28 cases of acute renal failure (ARF) with various causes. Among them 7 cases were thought to be originated from myoglobinuric ARF due to rhabdomyolysis. The causes of rhabdomyolysis were burns in one case, crush injury in one case, marathon running in one case, hypoxygenation from acute adrenal insufficiency in 2 cases and drugs in 2 cases. The serum and/or urinary level of myoglobin (Mb) detected by radioimmunoassy were moderately or highly elevated at the initial phase of ARF in these 7 cases. Also, there were hematest positive dark urine and dehydration of various degrees. There were no constant tendency in the serum level of uric acid, calcium, potassium in our cases with myoglobinuric acute renal failure (Mb-ARF), althought these parameters were fairly abnormal in Mb-ARF in the previous reports. Five cases received hemodialysis and two cases were treated conservatively. Six cases recovered completely from ARF and one case due to haloperidol induced Mb-ARF died, although frequent hemodialysis were performed. It was concluded that (1) Mb-ARF might be a considerably common cause of ARF, (2) measure-ment of serum and/or urine Mb might be very sensitive diagnostic tool for the differentiation of etiology of ARF. (3) However, Mb-ARF must be carefully differentiated from the acute exacerbation of chronic renal failure (CRF), since in patients with CRF the serum level of Mb were considerably high due to the disturbance of urinary excretion of Mb, (4) The outcome of Mb-ARF was relatively good.