We have studied ten phenotypically similar patients with complete androgen insensitivity. All of the patients tested had significantly elevated serum luteinizing hormone and plasma androgens within or above the normal adult male range. On the basis of specific dihydrotestosterone binding by skin fibroblasts, we identified two subgroups. Six patients from five different families had undetectable dihydrotestosterone binding, while four patients from two families had normal binding activity. Our results indicate that within the clinical syndrome of androgen insensitivity there are at least two distinct genetic variants. These variants may result from allelic mutations of the same X-linked gene specifying the dihydrotestosterone receptor or, alternatively, from mutations of separate genes both being essential for androgen action in responsive cells.