The concept of an inverse relationship between life span of adult Drosophila and their developmental temperature is probably the result of an unwarranted generalization. Rather, in a wild-type laboratory strain the present study revealed a plateau phase in this relationship between 16 and 29 ° C in which life span of both male and female flies was roughly independent of developmental temperature. Below and above this range, life span dropped drastically, development being impossible below 12 and above 32.5 °C. Simultaneous study of growth characteristics showed that the plateau phase corresponded to a ‘physiological’ range of developmental temperature, development being apparently disturbed outside that range. Within that physiological range, the growth rate of the flies varied 2-fold, while life span remained constant corroborating our previous conclusion that growth rate per se does not determine life span.