To test the effects of exercise on indices of protein metabolism, 8 sedentary, young women performed single bouts of prolonged submaximal and intermittent supramaximal exercise. The excretion of 3-methylhistidine, urea and creatinine in 24-hour urine samples was constant over the 11 -day experimental period, although the plasma urea concentration was elevated in blood samples obtained immediately after and 6 h following the prolonged exercise only. The results suggest that the acute exercise described here has a minimal effect on protein metabolism, and does not lead to a noticeable change in myofibrillar protein degradation in young women.