Rats and hamsters of both sexes were divided into exercise and non-exercise groups with and without small amounts of sulfamerazine in the diet. In every case rats on exercise lived longer than their controls. The females outlived the males while hamster males lived slightly longer than females. Sulfamerazine had a significantly beneficial effect on life span of rats and apparently increased that of male hamsters. All rats fed sulfamerazine attained higher maximum weights than their controls. There was no consistent change in bone densities.