Fawn-Hooded (FH) rats on a normal protein intake develop focal glomerulosclerosis, proteinuria and hypertension and die prematurely because of renal failure. In the present study we examined the effect of a life long feeding of a low (12%)-protein (LP) diet and a high (36%)-protein (HP) diet on renal function, urinary protein excretion (U<sub>prot</sub>V), systolic blood pressure (SBP) and survival time. Compared to the LP diet, the HP diet initially raised the glomerular filtration rate (GFR) and the U<sub>prot</sub>V, while the SBP was about the same. The U<sub>prot</sub>V of rats on the HP diet increased steadily and the GFR started to decline after 40 weeks. The LP diet resulted in a prolonged period of stable renal function, limited proteinuria and an increased life span. In the 2nd year of life, the level of hypertension was less in FH rats on the HP diet. Throughout the study there was no relationship between the SBP and the U<sub>prot</sub>V. The low UprotV in FH rats on the LP diet points to a lower level of glomerular capillary pressure. The attenuated development of glomerular hypertension on the LP diet slows down the subsequent renal damage in FH rats. This is in agreement with the view that glomerular hypertension is an essential hemodynamic derangement responsible for progressive deterioration of glomerular function. As in other rat models, i.e. renal ablation or unilateral nephrectomy, the LP diet slowed down the development of renal failure but did not prevent it.