A large outbred population of Drosophila melanogaster was subjected to artificial selection on lipid and glycogen storage. In three separate experiments, two replicates underwent sib selection for both increased and decreased storage. In the first study, flies were selected on the basis of total triacylglycerol for ten generations. This experiment resulted in no significant direct response, but there was a significant change in total body weight, underscoring the importance of concern for the allometric relationship between body weight and lipid content. In the second study, selection was performed for 15 generations on the percentage of body composition that was triacylglycerol. A significant direct response was obtained, and the two replicates revealed heritability estimates of 0·40 and 0·43. The third study selected glycogen content for 15 generations, and produced a significant response with heritabilities of 0·25 and 0·31. A series of 12 biochemical and enzyme kinetic traits was examined at five generation intervals in all experiments, and a number of correlated responses were detected. The results are interpreted with respect to the evolutionary constraints on energy storage evolution and the genetic basis of the allometric relationship between body weight and fat content.