Androgen resistance is thought to vary phenotypically from a normal female to an infertile male. Previous evaluation of infertile males has been limited to androgen receptor-binding affinity. The androgen receptor gene has been isolated, cloned, and studied extensively in patients with complete androgen insensitivity syndrome, but no comparative data are available on infertile males. To address this matter, the androgen receptor gene was studied in seven azoospermic males by use of the polymerase chain reaction and Southern blot hybridization. A partial gene deletion was found in one patient. This study provides the first molecular evidence of an abnormality in the androgen receptor gene in a phenotypic male with azoospermia.