AbstractWe studied the maternal effect for two enzymes of the pentose cycle, 6‐phosphogluconate dehydrogenase (6PGD) and glucose‐6‐phosphate dehydrogenase (G6PD), using a genetic system based on the interaction ofPgd−andZw−alleles, which inactivate 6PGD and G6PD, respectively. The presence and formation of the enzymes was investigated in those individuals that had not received the corresponding genes from the mother. We revealed maternal forms of the enzymes, detectable up to the pupal stage. The activities of “maternal” 6PGD and G6PD per individual increased 20‐fold to 30‐fold from the egg stage to the 3rd larval instar even in the absence of normalPgdandZwgenes. Immunologic studies have shown that the increase in 6PGD activity is due to an accumulation of the maternal form of the enzyme molecules. We revealed a hybrid isozyme resulting from an aggregation of the subunits of isozymes controlled by the genes of the mother and embryo itself. These results indicate that the maternal effect in the case of 6PGD is due to a long‐lived stable mRNA transmitted with the egg cytoplasm and translated during the development of Dros