An open, randomized, cross-over study was undertaken to assess the effects of lisinopril and nifedipine on albumin excretion, renal haemodynamics and segmental tubular reabsorption in overt diabetic nephropathy. The study consisted of a 4-week run-in period, a 3-week active treatment period, a 4-week wash-out period and a second 3-week active treatment period. Twelve patients with type 1 diabetes with albuminuria, mild to moderate hypertension and a serum creatinine level of less than 200 mumol l-1 were included. Lisinopril reduced albumin excretion from 1343 +/- 337 micrograms min-1 to 879 +/- 299 micrograms min-1 (P less than 0.01), whereas nifedipine was without effect, 1436 +/- 336 micrograms min-1 vs. 1319 +/- 342 micrograms min-1. Glomerular filtration rate (GFR) was unchanged by either drug. Both drugs increased effective renal plasma flow (ERPF) by about 20%. No differences between the drugs were observed with regard to their effect on renal haemodynamic parameters. By contrast, nifedipine exerted an inhibitory effect on several proximal tubular transport markers, whereas lisinopril was without effect. The different actions on tubular transport mechanisms exerted by lisinopril and nifedipine may contribute to the observed effect on albumin excretion.