The effect of a moderate ("soft") uncoupling of mitochondria on the lifespan and some parameters of biological age of Drosophila melanogaster strain Oregon was studied. Addition of the uncoupler 2,4-dinitrophenol (DNP) to the nutritional mixture of larvae significantly increased the average lifespan of the flies without changing their maximal lifespan. DNP significantly increased the rate of oxygen consumption by isolated mitochondria and tissue homogenates of the flies in state 4 (of Chance). DNP also decreased the activity of alcohol dehydrogenase (a parameter of flies' biological age) in the tissue homogenates, especially on octanol as the reaction substrate. However, being deprived of food the DNP-treated flies displayed a markedly decreased viability as compared to the control flies. On the whole, the results suggest that "soft" uncoupling of mitochondria may increase the lifespan.