Six patients with pure nonmosaic 46, XY gonadal dysgenesis (XY GD) and histocompatibility H-Y antigen titers in the normal male range (H-Y+) are presented. Clinical characteristics included a female phenotype, masculine skeletal characteristics, signs of virilization, and primary amenorrhea. AH individuals had unambiguous female external genitalia, a hypoplastic uterus, bilateral tubes, and streak gonads. Histomorphologic evaluation of the gonads revealed various abortive testicular and ovarian elements capable of steroid production. Gonadal tumors were found in 4 patients (gonadoblastoma, dysgerminoma, granulosa cell tumor, myxofibroma). Plasma and urinary androgens and basal and stimulated gonadotropin levels were elevated prior to gonadectomy. Data show that the presence of the H-Y antigen per se does not guarantee normal testicular organogenesis. It is hypothesized that defective H-Y antigen binding to its gonadal receptors triggers aberrant testicular differentiation in 46, XY H-Y+GD.