Complete androgen insensitivity syndrome is caused by X chromosome linked disorder resulting in a target organ insensitivity to androgen. Two variants have been described in this syndrome. In the first, the binding of [3H]dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one) to the androgen receptor is undetectable (receptor-negative), whereas in the second variant normal levels of androgen receptor are detectable but the binding of [3H] dihydrotestosterone to the androgen receptor is significantly thermolabile under certain conditions (receptor-positive). In receptor-negative cases, genetic disorders of the androgen receptor gene have been demonstrated. On the other hand, the genetic disorder of androgen receptor in receptor-positive cases is little known. In this study, the gene structure of androgen receptor in a receptor-positive case using a polymerase chain reaction technique is studied in the fibroblasts cultured from genital skin. The results demonstrate that the substitution of nucleotide (guanine-->cytosine) in exon G of the androgen receptor causes the replacement of an amino acid in position 820 (glycine-->alanine) which occurs in the hormone-binding domain of the androgen receptor. The substitution of nucleotide may explain the thermolability of the androgen receptor in a case with receptor-positive androgen insensitivity syndrome.