The rate of lipid peroxidation (LP) was measured in rotifers reared under conditions of continuous darkness (D:D), dietary restriction, vitamin e supplementation, or elevated temperatures. D:D, diet restriction, and vitamin e supplementation increased life span and caused a significant decline in lP; elevated temperatures decreased life span and increased LP. The addition of physiological levels of malonaldehyde, a product of LP, did not alter life span. The dietary uptake of paramecia, the food source for rotifers, did not change under the conditions of D:D, vitamin e supplementation, and elevated temperatures. These results suggest that the lp process is inversely related to longevity in the rotifer and that it appears to be involved in the aging process.