Male Wistar rats were maintained on four dietary regimens: fed ad libitum throughout life (A); fed intermittently either during the first year of life and ad libitum thereafter (RA) or vice versa (AR); and fed intermittently throughout life (R). Low body weights, low amounts of body components (protein, fat, moisture, and ash), and long life spans were observed in R. AR and RA lost or gained body weight, respectively, after dietary transfer and lived longer than A. Maximum body weight and the age at which it was attained were correlated positively with life span in A. Predicted mature body weight was correlated negatively with life span in R. RA and AR differed in growth and body composition, but their life spans were similar and intermediate to those of A and R. Increases in life span were obtained by intermittent feeding during all or part of the life span, but growth and body composition data did not consistently explain the mechanism of this effect.