Inherited adrenal and gonadal 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) deficiency is most likely caused by a mutation of the type II 3 beta-HSD gene. Cloning and sequencing of exons I-II, III, and IV and portions of the adjacent introns, amplified by polymerase chain reaction using primers specific for the type II gene, in one male pseudohermaphrodite with salt-wasting classic 3 beta-HSD deficiency congenital adrenal hyperplasia revealed the same mutation in all nine clones of exon IV consisting of a missense mutation at codon 248 [GTC(Val)-->AAC(Asn)] followed by a frameshift mutation at codon 249 [CGA (Arg)-->TA], resulting in a stop codon TAG, and normal sequences of exon I-II and III and the adjacent portions of introns. The same codon 248 and 249 mutations were found on one clone of his mother's DNA, but two other clones revealed normal sequences. These data indicate a homozygous combined missense/frameshift mutation in exon IV of the type II 3 beta-HSD gene resulting in severe salt-wasting adrenal and gonadal 3 beta-HSD deficiency in the patient.