The putative ACTH receptor gene has been identified on the basis of its tissue specific expression, structure, and limited expression data. We have expressed this gene in COS-7 cells and measured cAMP production in response to ACTH. An EC50 of 5.5 x 10(-9) M for ACTH (1-24) was determined. The S74I mutant ACTH receptor gene that associates with the syndrome of familial glucocorticoid deficiency had an EC50 of 67 x 10(-9) M. This discrepancy is consistent with the clinical data, and supports the hypothesis that this point mutation could account for the syndrome.