AbstractThe complete developmental program of glycerol‐3‐phosphate dehydrogenase in wild type Drosophila is described with respect to activity, isozyme expression, and GPDH‐specific CRM. Variants of this developmental program have been isolated from natural populations which affect the rate of accumulation of only the GPDH‐3 isozyme in both the larval and adult stages of development. This activity variation segregates as a single gene which is tightly linked to the structural element on Chromosome II, exhibits cis‐control, and is tissue specific in expression. This gene meets all the criteria for temporal regulat