Sequential urine specimens were obtained from 50 marathon runners before, immediately after and on 3 successive days following a marathon race. All prerace samples were normal, but 9 (18%) of the 50 postrace urinalyses showed gross (1 specimen) or microscopic (8 specimens) hematuria. No formed elements other than RBC were seen, and all abnormalities cleared by 48 h. Exercise-related hematuria appears to be a frequent, self-limited, and benign condition. Physicians should be aware of its occurrence and reserve extended testing for cases in which abnormalities persist beyond 48-72 hr.