AbstractTranscripts of the dopa decarboxylase (Ddc) gene accumulate within 4 h of the administration of 20‐OH‐ecdysone to mature larvae ofDrosophila.The increase can be explained as the sum of a direct steroid effect, independent of protein synthesis, and an indirect effect, dependent on proteins synthesized after an increase in the hormone titer. By contrast, the peaks of DDC activity in embryos, and perhaps in the first two larval instars and in imaginal discs as well, cannot be ascribed to any direct steroid effects. In fact, a decreasing hormone titer might be required before the Ddc gene can be expressed at these stages. The stage‐specific differences in the molecular mechanisms regulating Ddc gene activity may be reflected in the phenotype of an activity variant,Ddc+4. Molecular studies now underway on the variant Ddc gene might help us to understand the complex multifunctional region that we believe lies upstream of the gene and regulates its expression during develo