The effects of low-meat-protein diets on hypercholesterolemia and proteinuria were studied in rats with nephrotoxic serum nephritis. After an injection of nephrotoxic serum, rats were given either a 20% meat-protein diet (20M), an 8.5%-meat-protein diet (8.5M), or a valine-(0.05%)-supplemented 8.5%-meat-protein diet (8.5MV) for 12 days. Urinary protein excreted from the 20M-fed, nephritic control rats increased rapidly and linearly during the initial 3 days, and thereafter the high excretion rate was maintained for up to 12 days. Two low-meat-protein diets (8.5M, 8.5MV) commenced to suppress proteinuria 3 days after feeding and the suppression was preserved during the rest of the experimental periods. Compared with the 20M, both low-meat-protein diets significantly improved hypercholesterolemia induced in this nephritic model. These two diets significantly enhanced the fecal excretion of neutral sterols. They caused neither fatty liver nor severe growth retardation. These effects of 8.5MV were identical to those of 8.5M. The results suggest that low-meat-protein feeding, without amino acid supplementation, improves hypercholesterolemia and proteinuria in nephritis without severe protein malnutrition. The results also suggest that the hypocholesterolemic effect of the low-meat-protein diets may be, at least in part, attributed to increased fecal excretion of steroids.