Androgen insensitivity was demonstrated in two male siblings with partial masculinization of the external genitalia. They had a previously undescribed defect characterized postpubertally by high plasma testosterone and luteinizing hormone concentrations with low serum follicle-stimulating hormone levels. Studies in skin fibroblasts showed normal androgen receptor affinity and capacity for 5alpha-dihydrotestosterone (DHT), normal nuclear retention of the receptor-DHT complex, and normal conversion of testosterone to DHT.