The effect of inactivation of superoxide dismutase, by diethyldithiocarbamate, on life span, metabolic rate, superoxide dismutase activity, catalase activity, inorganic peroxide concentration and glutathione levels in adult male houseflies was determined. The general objective was to examine the role of free radical defenses in the aging process. Houseflies were administered 0. 1 and 10 mM diethyldithiocarbamate in their drinking water. Administration of diethyldithiocarbamate caused an extension in the average life spans of the populations while the metabolic rates were depressed. Superoxide dismutase activity was significantly reduced. Inorganic peroxide concentration and catalase activity declined in rough correspondence to the decrease in the metabolic rate. The levels of reduced glutathione were significantly elevated whereas oxidized glutathione concentrations remained relatively unaffected. The results are interpreted to indicate that a decrease in superoxide dismutase activity in the housefly, by diethyldithiocarbamate administration, is compensated by an elevation in reduced glutathione levels and reduction of oxygen consumption, suggesting the existence of alternative free radical defenses in vivo.