Heat stroke in distance runners is increasing in frequency. A case is reported of a 41-year-old man who collapsed during a 10-km "fun run" held when the temperature was 31.6 degrees C and the humidity 80%. Acute renal failure (serum creatinine level 1530 mumol/l [17.3 mg/dl]), rhabdomyolysis, disseminated intravascular coagulation and hepatic damage complicated the clinical picture. Repeated peritoneal dialysis and one cycle of hemodialysis because of a very high serum level of uric acid (1.23 mmol/l [20.7 mg/dl]) were required. Although the illness was prolonged, recovery was almost complete, and 4 months after the man's collapse the serum creatinine level had fallen to 133 mumol/l (1.5 mg/dl).