We studied the effect of repeated heavy physical activity on glomerular filtration rate (GFR) in healthy, uninephrectomized and experimentally uremic mice. Exercise consisted of running uphill in the inner surface of a rotating cylinder in ideal environmental temperature. In the control groups, no extra physical activity was imposed. In sham-operated and nephrectomized mice, GFR rose significantly following training. By contrast, GFR did not change significantly in the exercised mice with experimental renal failure 24 h following the last exercise session. During the same period, no significant change was observed in GFR of any of the control groups. Following training in each experimental group, mean aortic blood pressure as well as fractional kidney weight (kidney weight/body weight) were not different from the respective controls. Our results indicate that the capacity to augment GFR by physical training is dependent upon the amount of remaining functional renal tissue.