Two adult brothers became ill within 48 hours of each other, and both had severe myoglobinuria. One brother died of oliguric renal failure. The other did not have renal failure and survived. Acute influenza A infection was documented serologically and from throat washings in the surviving brother, and by isolation of the influenza A virus from throat cultures and lung tissue of the brother who died. It is not certain whether a genetic myopathy made these brothers susceptible to viral-induced myoglobinuria, but a normal response of venous lactate to ischemic work excluded lack of phosphorylase or phosphofructokinase as a cause of the myoglobinuria in the surviving brother. Neither brother had a history of recurrent episodes of myoglobinuria precipitated by exercise, cold, or fasting, thus making carnitine palmityl transferase deficiency unlikely.