The antiproteinuric effect of angiotensin converting enzyme (ACE) inhibition in patients with renal disease is well known, but the results of clinical studies appear to vary considerably from a partial decrease to a fall of 100% in urinary protein excretion. This may have been due to the use of different doses of ACE inhibitor, different renal pathology and non-standardized sodium intake. In 16 proteinuric patients with biopsy-proven IgA nephropathy, with normal renal function and blood pressure, maintained at controlled sodium intake < or = 80 mEqII, the efficacy of increasing doses of the ACE inhibitor lisinopril was studied. The lisinopril doses were 5, 10, 15 and 20 mg, administered for 4 weeks. Between each dose increment a placebo period of 3 weeks was interposed. Proteinuria stepwise decreased from the control period by 39%, 44%, 61% and 67% with lisinopril at 5, 10, 15 and 20 mg, respectively. The blood pressure decreased by 22% with lisinopril 5 mg; a similar fall was observed with the dose increment. Although the glomerular filtration rate remained unchanged, the renal plasma flow increased by 21%, 26%, 24% and 28% and the filtration fraction increased by 28% mean. The ACE plasma levels decreased by 33%, 64%, 76% and 83%. A close correlation was found between an increase in lisinopril dosage and the fall in urinary protein excretion (r = 0.88, p < 0.001). The antiproteinuric effect of lisinopril is dose-related and may be attributable to some extent to the fall in systemic (and intraglomerular) blood pressure, but it is best attributed to the modification of glomerular sieving function.(ABSTRACT TRUNCATED AT 250 WORDS)