The effects of the angiotensin converting enzyme (ACE) inhibitor lisinopril on blood pressure, proteinuria and renal hemodynamics were evaluated in 13 patients with renal disease of different origin. A comparison was made with the effects of conventional antihypertensive therapy. Both drug regimens significantly lowered blood pressure, while only after 12 weeks of treatment with lisinopril, blood pressure was significantly lower than during conventional therapy. Lisinopril reduced proteinuria (by 61 +/- 40%), whereas conventional therapy had no significant effect on protein excretion. During the first eight weeks of treatment with lisinopril, there was a comparable degree of blood pressure reduction with both treatment regimens, whereas urinary protein loss was significantly less during ACE inhibition. There was only a nearly-significant positive correlation between the fall in proteinuria during lisinopril and the concomitant decrease in mean arterial pressure. Glomerular filtration rate decreased from 26.3 +/- 11.6 to 20.6 +/- 9.4 ml/min during treatment with lisinopril. This decrease was not correlated with the fall in proteinuria. A significant positive correlation existed between the fall in urinary protein excretion and both the decrease in overall renal vascular resistance, and the fall in filtration fraction. Although blood pressure lowering by itself could contribute to the antiproteinuric effect of lisinopril, our results suggest that this effect of ACE inhibition is also due to efferent (postglomerular) vasodilation. We conclude that the ACE inhibitor lisinopril effectively reduces blood pressure and proteinuria in renal disease. The latter effect is not only the result of a lower blood pressure, but is probably also due to a fall in intraglomerular capillary pressure.