The purpose of this investigation was to further elucidate the relationship between metabolic rate and life span by studying the effect of experimentally varied metabolic rate on in vitro lipid peroxidation, fluorescent age pigment accumulation, and aging in the adult milkweed bug. The metabolic rate was altered by housing the insects at 18 degrees, 25 degrees, and 30 degrees C. The life span of insects was inversely related to the ambient temperature. Metabolic rates, before the period of 10% mortality, were greater at the elevated temperatures, but in the last trimester of life the rates were higher at 25 degrees C than at 30 degrees C. The total average amount of oxygen consumption during the entire life span of the insects raised at different temperatures was statistically similar. Lipid peroxidation potential of the tissues and concentration of fluorescent age pigment increased with age at significantly faster rates in organisms raised at relatively higher temperatures. The results suggest a positive correlation between metabolic rate, aging, lipid peroxidation potential, and fluorescent age pigment concentration and are interpreted to support the concept that aging may be modulated by the rate of oxygen consumption.