Activities of flavin-linked alpha-glycerophosphate, succinic, and malate dehydrogenases were studied in the flight muscles of male houseflies of different ages. Enzyme levels are higher in 4, 14, and 21 day old flies as compared to 7 and 18 day old flies. Results of this study indicate that dehydrogenase activity is apparently unrelated to the age-related decline in flight activity of the housefly.