Androgen insensitivity syndrome (AIS) is associated with a wide range of quantitative or qualitative defects in the androgen receptor (AR). In some patients with AIS, however, no defects are detectable in the ligand-binding properties of the AR. We have analyzed the ARs of two unrelated patients with this category (termed 'receptor-positive type') of AIS. Sequence analysis of these patients' AR gene revealed single amino acid substitutions (579Cys(TGC)-->Phe(TTC) and 582Phe(TTC)-->Tyr(TAC)) in exon B encoding the first zinc finger of the DNA-binding domain of the AR. These mutations have not been previously reported. Moreover, cotransfection assays and mobility shift assays revealed that these patients' mutant ARs had defective transcriptional activity of the target gene because of impaired DNA-binding ability to the androgen-responsive element. These findings strongly indicate that these mutations are responsible for the pathogenesis of AIS in these patients.