This study compared the effects of feeding a high protein (HP) and low protein (LP) diet to healthy cats and cats with surgically induced chronic renal failure. Results showed that cats fed the LP diet had reduced serum urea nitrogen concentrations, despite lower glomerular filtration rates. Cats fed the HP diet consumed significantly more calories and consequently weighed more than did cats fed the LP diet, probably due to higher palatability. As a result of the lower caloric intake in cats fed the LP diet, these cats were protein and calorie restricted, compared with cats fed the HP diet. Mean haematocrit and mean serum albumin concentration were significantly lower in control cats and in cats with CRF fed the LP diet, compared with control cats and cats with CRF fed the HP diet.