This study investigated the clinical and biochemical features of acute renal failure in marathon runners. Over a period of 18 years (1969-1986), 19 patients were admitted to the renal unit. The histories and biochemical data of 4 patients seen in 1986 are described. The pathophysiology of acute renal failure is multifactorial and is the combined effect of rhabdomyolysis, dehydration, hypotension, nonsteroidal anti-inflammatory drugs, and hyperuricaemia. Efforts to correct dehydration have resulted in a decrease in the incidence of acute renal failure. The use of nonsteroidal anti-inflammatory drugs is to be deprecated and efforts should be made to publicize this harmful effect.