Nephrotic patients with persistent proteinuria also have various lipid abnormalities that may promote atherosclerosis and more rapid progression of renal disease. We aimed to find out whether dietary manipulation can correct the hyperlipidaemia found in these patients. After a baseline control period of 8 weeks on their usual diets, 20 untreated patients with chronic glomerular diseases, stable long-lasting severe proteinuria (5.9 [SD 3.4] g/24 h) and hyperlipidaemia (mean serum cholesterol 8.69 [3.34] mmol/l) ate a vegetarian soy diet for 8 weeks. The diet was low in fat (28% of total calories) and protein (0.71 [0.36] g/kg ideal body weight daily), cholesterol free, and rich in monounsaturated and polyunsaturated fatty acids (polyunsaturated/saturated ratio 2.5) and in fibre (40 g/day). After the diet period the patients resumed their usual diets for 8 weeks (washout period). During the soy-diet period there were significant falls in serum cholesterol (total, low-density lipoprotein, and high-density lipoprotein) and apolipoproteins A and B, but serum triglyceride concentrations did not change. Urinary protein excretion fell significantly. The concentrations of all lipid fractions and the amount of proteinuria tended to return towards baseline values during the washout period. We do not know whether the favourable effect of this dietary manipulation on proteinuria was due to the qualitative or quantitative modifications of dietary protein intake or was a direct consequence of the manipulation of dietary lipid intake.