Stearoyl-CoA desaturase gene 1 (scd1) mRNA levels were induced during the 1st day of 3T3-L1 differentiation. scd1 expression had previously been observed only in late-stage differentiation, during the period of triacylglycerol accumulation. The induction of 3T3-L1 differentiation requires treatment with insulin, dexamethasone, and an agent that increases intracellular cAMP levels. Treatment of preadipocytes with cAMP-elevating agents caused an increase in scd1 mRNA concentrations. Insulin and dexamethasone had no effect on scd1 mRNA expression in preadipocytes. The increase in mRNA resulted from transcriptional activation of the scd1 gene. 8-Bromo-cAMP treatment of differentiated adipocytes had no effect on scd1 mRNA levels, suggesting a preadipocyte-specific effect. The increase in scd1 mRNA occurred maximally after 6 h of cAMP treatment and was shown to require protein synthesis. Deletion and mutagenesis analyses have localized the cAMP response to sequence within the first 250 base pairs of the 5'-flanking region of the scd1 gene. Treatment with phorbol ester enhanced the induction of scd1 mRNA by cAMP, suggesting the involvement of AP-2 as a mediator of the cAMP response. The induction of scd1 expression by cAMP during early differentiation was distinct from that observed during late adipocyte development. This early expression presents a novel regulated function of scd1 during the differentiation process, independent of its lipogenic role in late adipocyte development. The induction of scd1 also introduces a role for cAMP in 3T3-L1 differentiation.