OBJECTIVE: Our purpose was to establish the incidence of point mutations of the 21-hydroxylase gene (CYP21) in hyperandrogenic women with and without a 17-hydroxyprogesterone response to corticotropin stimulation above normal but below those levels associated with nonclassic adrenal hyperplasia. STUDY DESIGN: We studied 22 patients with hirsutism or hyperandrogenic oligoovulation: eight with an exaggerated net increase in 17-hydroxyprogesterone (i.e., change in 17-hydroxyprogesterone between 8.8 and 36 nmol/L) and 14 with a normal change in 17-hydroxyprogesterone. Large deletions of the 21-hydroxylase gene were evaluated by laser densitometry. Point mutations were detected with the polymerase chain reaction and dot blot hybridization analysis and included 30 Leu, intron-2 (G), 8 bp deletion exon-3, 172 Asn, 236-237-239 exon-6, 281 Leu, 318 stop, 339 His, 341 Trp, 356 Trp, and 453 Ser. RESULTS: Four patients with an increase in 17-hydroxyprogesterone carried a 281 Leu mutation, one patient had an intron-2 (G) mutation, and one had a complete deletion of CYP21. Only two of these patients demonstrated no obvious abnormality of CYP21. In contrast, only one of the control patients demonstrated a CYP21 abnormality, a significant difference (p < 0.001). CONCLUSIONS: These findings suggest that the majority of hyperandrogenic women with an exaggerated 17-hydroxyprogesterone response to corticotropin stimulation are heterozygotes (carriers) for inherited defects of CYP21. Whether these mutations are incidental to the androgen excess or predispose to the development of this disorder remains to be determined. © 1995.