The aim of this study was to investigate whether the renoprotective effect of angiotensin–converting enzyme inhibitors (ACEIs) following 5/6 renal mass reduction is due in part to the potentiation of kinins. Three groups of rats with 5/6 renal mass reduction were studied during the 14 weeks following surgery. One group received no therapy (control); the second group was treated from the beginning with the ACEI ramipril (1 mg/kg/day) added to the drinking water, and the last group received ramipril plus a β<sub>2</sub>–bradykinin antagonist, HOE 140 (500 μg/kg/day) via osmotic minipumps. Plasma creatinine did not change in any group during the study. Urinary protein excretion rose in the controls from 9.18±1.6 to 45.0±5.6 mg/24 h at the end of the study. In ramipril group proteinuria was prevented (initial 7.5±1.0 and final 8.6±0.8 mg/24h). The effect of ramipril was abolished by HOE 140 (initial 11.6±2.0 and final 38.9±11 mg/ 24h). The systolic blood pressure of the controls increased from 106±2 to 144±5mmHg at the 14th week. Ramipril abolished the increase in systolic blood pressure. The effect of ramipril was reverted by HOE 140 (initial 108±2 and final 140±9 mmHg). Control rats had more severe histopathologic changes. Those animals receiving ramipril + HOE 140 displayed less severe glomerular changes, while rats treated only with ramipril had mild alterations. Thus the glomerular injury score was 2.11±0.32 for controls, 1.53±0.52 for rats treated with ramipril + HOE 140, and 0.06±0.04 for rats treated only with ramipril. The glomerular area was 20,886±1,410, 19,693±2,200 and 14,352±3,200 μm<sup>2</sup>, respectively, for the 3 groups. These results suggest that the protective effect of ACEIs in the development of chronic renal failure is partially mediated by kinins.