One-dimensional electrophoresis was performed on extracts of flies collected from across all ages. Protein gel patterns were compared for two strains of Drosophila melanogaster with distinctly long and short adult life spans that result from different alleles of longevity genes. An inter-strain difference was observed in the changes in protein pattern in the 77 kDa region in period of day 0-5 after emerging. We propose that the protein involved is a product of autosomal longevity alleles A1 and A2 at the Jm A locus and is related to development of longevity potentials in the preimaginal stage.