Two siblings with the classical phenotype of complete androgen insensitivity syndrome (CAIS) and increased total cellular androgen receptor concentrations in genital skin fibroblasts (GSF) are described. Testosterone biosynthesis was normal, and there was no evidence of 5 alpha-reductase deficiency. Specific binding of [3H]dihydrotestosterone ([3H]DHT) in GSF was 7 SD above the mean value in normal fibroblast strains [maximum binding, 775 +/- 185 X 10(-18) mol/micrograms DNA (mean +/- SD)]. Binding at 40 C was stable, and the androgen-receptor complex dissociated at a normal rate (t1/2, 85 min). The androgen-receptor complex from GSF cytosol sedimented at 5-6S on sucrose density gradients in the presence of sodium molybdate. In a whole cell binding assay, the percentage of [3H]DHT that bound to a crude nuclear pellet was 60%. Preincubation of GSF with 2 nM [3H]DHT for 20 h before the standard 1-h whole cell binding assay produced a further augmentation in elevated total cellular androgen receptor concentrations. A new variant of CAIS is described which is characterized by an increased concentration of androgen receptors that appear to be quantitatively and qualitatively normal. Augmentation of the receptor by androgen suggests that the gene coding for the androgen receptor is intact and does not account for the androgen insensitivity.