Previous investigations suggest that increased life span of calorie-restricted rodents is a function of caloric intake rather than the macro- or micronutrient composition of the diet. However, the dietary source of carbohydrate has not been widely investigated. We hypothesized that the dietary carbohydrate source may affect the life span of rats independent of caloric restriction. This hypothesis was tested in male Fischer 344 rats fed ad libitum or restricted to 60% of ad libitum, an isocaloric diet containing 14% protein, 10% fat, and 66% sucrose or cornstarch. Body weights of the ad libitum- and restricted-fed sucrose rats were consistently greater throughout the experimental period compared to diet-matched animals. Food intake did not differ significantly. The survival curves of ad libitum starch- vs sucrose-fed rats were significantly different. That is, the mean, median and upper 10th percentile survival were significantly greater in the ad libitum starch- vs sucrose-fed rats (mean life span: cornstarch-fed, 720 +/- 23 days; sucrose-fed, 659 +/- 19 days). Calorie-restricted starch-fed rats had poorer early life survival, and no significant increase in mean life span compared to ad libitum cornstarch-fed animals (726 vs 720 days). These animals did, however, have the greatest upper 10th percentile survival of all four experimental groups. Mean life span of calorie-restricted sucrose-fed rats was significantly greater than that of all other groups (890 +/- 18 days). The differences in survival rates between sucrose- and cornstarch-fed animals could not be attributed to the effects of carbohydrate source on body weight, energy absorption, or on the timing and severity of the pathological lesions normally associated with aging and/or caloric restriction in this species. These data support the hypothesis that the dietary source of carbohydrate, i.e., sucrose vs cornstarch, can significantly affect life span independently of caloric intake.