The extended longevity phenotype (ELP) characteristic of our selected long-lived strain of Drosophila is brought about by a delayed onset of senescence which occurs in the young (5-7 day) adult. Genetically competent animals will not express the resistance to exogenous paraquat characteristic of the ELP as adults unless they develop in a particular larval environment. This induction leads to a series of coordinated increases in their antioxidant defense system mRNA levels and in their enzyme activities. Not all genes show such changes. These increases in antioxidant gene product levels appear to be functional, as witnessed by the fact that the long-lived animals show an increase in their resistance to exogenous paraquat at that same time. Aminotriazole-induced destruction of catalase activity in the long-lived animals results in the loss of their increased resistance to paraquat. The non-induced control animals do not show such elevations in antioxidant defense system elevations, and shortly thereafter show a significant decline in their paraquat resistance followed by the subsequent loss of certain behavioral traits diagnostic of senescence.