The influence of gamma-irradiation and 5-bromo-2'-deoxyuridine (BUDR) on the life span and behaviour (in photoactivity test) of D. melanogaster was studied. It was found that gamma-irradiation resulted in decrease of life span. However the form of survival curves changed only under exposure to doses higher than 500 Gy. Treatment with BUDR distorted the form of survival curves and caused death of insects immediately after exclusion. It also caused abrupt decrease in photoactivity of insects, while irradiation even with very high doses did not affect this feature. It is proposed that initiating substrat in drosophila aging is DNA of nerve cells. The possible relationship between aging regularities and evolutional extinction of eucaryotic species is discussed.