Our previous findings indicated that a major characteristic of aging organisms is a decrease in reducing capacity. Our objectives were to correct this impairment by administration of nordihydroguaiaretic acid (NDGA), a potent reducing agent, and to determine the effect on adult longevity of the mosquito. NDGA supplements were included in the axenic larval medium or adult diet of mosquitoes of different ages. The mean adult life spans of both sexes increased 42-64% over controls (P less than 0.025), and the most effective doses were 0.001% for females and 0.005% for males. This NDGA effect was dependent on the age when feeding was initiated, since only biosynthetically active larvae and young adults were responsive. Also the effect was not due to dietary restriction. These results confirm the life span-enhancement effect of NDGA using defined conditions and establish the importance of redox status in the aging process.