The development of age-associated proteinuria and renal disease was studied in groups of male Wistar rats fed 12.5, 25, 50 and 75 kcal of food/day, respectively, and in calorie-restricted (40 kcal/day) rats receiving diets rich in fat, protein or carbohydrate. Proteinuria developed faster, kidneys were larger and the incidence of glomerular lesions and proteinaceous casts was greater in rats eating high calorie diets of 50 kcal/day or more. High protein diets, even when calorie-restricted, increased protein excretion and the incidence of glomerular lesions. In old rats acute food restriction (25 kcal/day) decreased protein excretion by 40 % in 1 week, with no further reduction in the 2 week. Life duration was greatest in rats fed 50 kcal/day.