Long-term dietary restriction programs which retard aging processes in rodents usually involve meal eating rather than the nibbling pattern of food intake of ad libitum fed rodents. Thus, the possibility arises that the antiaging action may at least in part result from an altered temporal pattern of food intake. This possibility was investigated using male F344 rats maintained on the following dietary regimens: Group A rats fed ad libitum; Group B rats fed 60% the ad libitum intake in a single meal at 1500 h; Group B-2 rats fed 60% of the ad libitum intake in two meals (0700 h and 1500 h). The diurnal pattern of plasma corticosterone concentration differed among the groups as did that of the plasma glucose concentration. The median length of life and age of tenth percentile survivors were similar for Group B and B-2 rats and much greater than those for Group A rats. Both modes of dietary restriction influenced ageassociated disease processes in a similar fashion. Thus, although the temporal pattern of food intake influenced circadian rhythms of food-restricted rats, it did not significantly affect the antiaging action.