Kinetin, a cytokinin plant growth hormone, retards senescence in plants, delays aging in human cells in culture, slows down development of insects and prolongs their lifespan. We have now observed that the increased longevity of Kn-fed Zaprionus fruitflies was accompanied by an increase in the specific activity of catalase during developmental stages and in adult insects. In addition, the egg laying capacity of Kn-fed fruitflies was reduced drastically as compared with those kept on a normal diet. These results support the view that improved maintenance of the soma and prolongation of its life is achieved at the cost of decreased reproductive activity.