The effects of maturation and aging on cell stability and maintenance of protein expression have been examined in adult Drosophila melanogaster. Counting the number of cells present in the antenna of the adult fly revealed little loss in cell number with aging. Enhancer map-marked genes expressing beta-galactosidase (beta-gal) in the antenna and an Rh1 opsin reporter gene construct expressing beta-gal in the R1-6 photoreceptor cells of the compound eye revealed no alteration in spatial distribution or amount of beta-gal with aging. A heat shock-inducible promoter coupled to the expression of beta-gal, hsp70-lacZ, revealed that the rate and amount of induction of beta-gal after heat shock is preserved during aging but the rate of decay of beta-gal may be slightly delayed in older animals. These studies suggest that the ability to express a reporter protein, beta-galactosidase, is preserved in at least a subset of cells in the aging fly.