The purpose of this study was to compare the angiotensin converting enzyme (ACE ) inhibitor ramiprilat to captopril with respect to its efficacy in decreasing blood pressure (BP) and increasing renal blood flow (RBF),when administered intravenously (i. v. ),or as in a separate group of experiments when given intrarenally (i. a ). Thirty-four anesthetized rabbits were employed in 3 groups of experiments in which BP and RBF were the measured parameters. In Group I,ramiprilat (1 mg/kg and 0. 5 mg/kg· h-1 i. v. )decreased BP from 107 ± 5 to 83± 8 mmHg and increased RBF from 33± 3 ml/min to 44± 7 ml/min. Captopril (2 mg/kg and 1 mg/kg· h-1 i. v. ) decreased BP from 99 ± 6 to 77 ± 8 mmHg and increased RBF from 30±1 to 42± 3 ml/min. Both ramiprilat and captopril abolished the pressor effect and greatly attenuated the renal vasoconstrictor response to injected angiotensin I. When the ACE inhibitors were administered in graded doses i. a. (Group Ⅱ ), they caused a similar increase in RBF , but a lesser decrease in BP compared to those when given i. v. Ramiprilat was more potent than captopril by either route of administration. In the presence of HK2 kinin receptor blockade by HOE 140 (Group Ⅲ ), the effect of ramiprilat and captopril on BP and RBF did not differ from that in Group Ⅱ. In conclusion, ramiprilat and captopril cause a similar renal hemodynamic effect and decrease in BP,and there is no difference in their efficacy either in the presence or absence of BK antagonism. The purpose of this study was to compare the angiotensin converting enzyme (ACE) inhibitor ramiprilat to captopril with respect to its efficacy in decreasing blood pressure (BP) and increasing renal blood flow (RBF), when administered intravenously (iv), or as in a separate group of experiments when given intrarenally (i. a). Thirty-four anesthetized rabbits were employed in 3 groups of experiments in which BP and RBF were the measured parameters. In Group I, ramiprilat (1 mg / kg and 0.5 mg / kg · h-1 iv) decreased BP from 107 ± 5 to 83 ± 8 mmHg and increased RBF from 33 ± 3 ml / min to 44 ± 7 ml / min Captopril (2 mg / kg and 1 mg / kg · h-1 iv) decreased BP from 99 ± 6 to 77 ± 8 mmHg and increased RBF from 30 ± 1 to 42 ± 3 ml / min Both ramiprilat and captopril abolished the pressor effect and greatly attenuated the renal vasoconstrictor response to injected angiotensin I When the ACE inhibitors were administered in graded doses ia (Group Ⅱ), they caused a similar increase in RBF, but a lesser decrease in BP compared to those when given iv Ramiprilat was more potent than captopril by either route of administration. In the presence of HK2 kinin receptor blockade by HOE 140 (Group III), the effect of ramiprilat and captopril on BP and RBF did not differ from that in Group II. In conclusion, ramiprilat and captopril cause a similar renal hemodynamic effect and decrease in BP, and there is no difference in their efficacy either in the presence or absence of BK antagonism.