Strenuous physical exercise causes transient proteinuria and renal hemodynamic changes: decrease of renal blood flow and to a lesser extent of the glomerular filtration rate, and an increase of the filtration fraction. However, the mechanisms of these modifications are still poorly understood. In order to elucidate them we performed maximal exercise tests on 8 untrained healthy volunteers after inhibition of the renin-angiotensin system (RAS) by captopril, the sympathetic nervous system by a beta-blocking drug (acebutolol) or an alpha-blocking drug (prazosin) and the prostaglandin system by indomethacin. Urinary albumin excretion was measured in every subject first at rest (AB) and then after exercise (AA) performed successively without and with blockade by each of theses drugs. AA-AB difference in the captopril test (12.04 +/- 6.11 micrograms/min) compared to that in the control test (68.91 +/- 25.18 micrograms/min) was significantly reduced (p less than 0.02). This difference remained unchanged after acebutolol (59.87 +/- 21.91 micrograms/min, p = 0.62), prazosin (35.23 +/- 27.80 micrograms/min, p = 0.21) and indomethacin (55.21 +/- 28.43 micrograms/min, p = 0.35). There was a negative correlation between the lowering of AA elevation and the rise in plasma renin activity in the captopril test (r = 0.64; p less than 0.03). Only acebutolol decreased systolic blood pressure significantly. These results suggest that the RAS plays a major role in postexercise proteinuria. We hypothesize that stimulation of this system induces an increase of efferent glomerular artery constriction and consequently of glomerular transcapillary pressure and the filtration fraction. Captopril seems able to prevent these hemodynamic changes.