We have studied labium majus skin fibroblast strains from six unrelated, previously unreported, patients with complete androgen insensitivity (CAI). Four have markedly reduced specific 5 alpha-dihydrotestosterone-binding (DHT-binding) activity (receptor-negative). The other two (receptor-positive) have normal activities in whole-cell homogenates, the 100,000g supernatant of cell sonicates prepared in 0.4 MKCl, purified whole nuclei, and the nuclear fraction that resists extraction with 0.4 MKCl. In one of the two, the DHT-binding macromolecules in the cytosol and 0.4 M KCl-extractable nuclear fraction have normal molecular sieving profiles and binding activities. One of the receptor-positive patients has maternally related affected relatives in three successive genetations. Appreciable unexplained interexperimental variation of the DHT-binding activities in genital skin fibroblast strains demands that multiple assays be performed on a strain before its receptor status is classified quantitatively. In our experience to date with genital skin fibroblasts, four of 13 propositi with CAI have been receptor-positive.