Life spans of poikilotherms like the housefly are shortened by elevation of ambient temperature. The objective of this study was to examine the possible involvement of active oxygen species in temperature induced life-shortening of the adult male housefly. Effects of varied ambient temperature, 20 degrees C and 28 degrees C, on life span, cyanide-resistant respiration, H2O2 concentration, superoxide dismutase (SOD) and catalase activities and glutathione (GSH) concentration were examined. Average life span of flies raised at 28 degrees C was about 52% lower than those raised at 20 degrees C. Rate of cyanide-resistant respiration, an indicator of oxygen free radical generation, was higher in flies raised at 28 degrees C, whereas steady-state concentration of H2O2 was decreased at this temperature. Catalase activity and GSH concentration were lower at 28 degrees C while SOD activity was unaffected by the ambient temperature. Results of this study suggest that life-shortening effects of elevated ambient temperature may be due, in part, to increased oxidative stress.