alpha-Glycerophosphate dehydrogenase (GPDH) expression during the complete development and aging of Anopheles stephensi has been studied by electrophoretic and spectrophotometric techniques. Single gene locus seems to govern the developmental expression of three isozymes numbered from GPDH-1 to GPDH-3 in order of decreasing mobility. GPDH-3 was present in all the stages of development. GPDH-1 disappeared during senescence. GPDH-2, the band of intermediate mobility, was adult specific. GPDH-1 has been indicated to be more suitable for energy metabolism and GPDH-3 for lipid biosynthesis. Three codominant alleles control the four electrophoretic variants revealed in the laboratory strain. Quantitatively, the activity of GPDH continuously increased during development and showed its peak on day-4 adults of both sexes. However, the activity decreased during senescence. Tissue and sex specific differences in isozymes pattern have also been analysed. Changes in isozymes and specific activity have been correlated with the various physiological and morphological events occurring during development.