In this study we compared the antihypertensive and antiproteinuric efficacies of an angiotensin-converting enzyme inhibitor and of conventional treatment consisting of a beta blocker and a diuretic in 13 patients with biopsy-proven glomerulonephritis and a proteinuria of more than 2 g/24 h. Ten of these 13 patients were normotensive. None had diabetes mellitus. In a randomized cross-over design with two treatment periods of 6 weeks, each preceded by a washout period of 4 weeks, patients were treated with benazepril (20 mg o.d.) and the combination of metoprolol (200 mg o.d.) and chlorthalidone (25 mg o.d.). At the end of the treatment periods with benazepril or metoprolol/chlorthalidone mean arterial pressure was lowered to a similar degree by 7.4 (mean, 95% confidence interval 2.0-12.7) and 9.7 (5.7-13.7) mmHg respectively. Both treatment modalities caused similar reductions in proteinuria, being 3.4 g/24 h (mean, 95% confidence interval 2.1-4.8) on benazepril and 3.2 (1.2-5.1) g/24 h on metoprolol/chlorthalidone. Glomerular filtration rate and renal plasma flow were slightly less during metoprolol/chlorthalidone treatment. Subgroup analysis of normotensive patients gave similar results. In conclusion, in these patients with glomerular disease angiotensin-converting enzyme inhibition was not more effective than the conventional treatment with the combination of a beta blocker and a diuretic in reducing blood pressure and proteinuria. Both treatments reduced proteinuria not only in hypertensive, but also in normotensive patients.