Endocrine studies of a virilized adolescent patient with massive ovarian edema are reported. The histologic features of the affected ovary consisted of diffuse edematous stroma with scattered islands of lutein-like cells and no evidence of recent ovulation. Plasma concentrations of progesterone and 17-hydroxyprogesterone (17-OHP) in the peripheral and left ovarian veins and their ovarian-peripheral vein gradients were above the range observed during normal follicular phase. The considerable increase in the ovarian vein concentrations of both steroids observed after adrenocorticotropic hormone administration was noteworthy as a direct effect of this hormone on the ovarian synthesis of steroids has not previously been observed. Peripheral vein levels of testosterone (T) were increased. The secretion of T by the ovary was demonstrated by its elevated levels in the ovarian vein and in the ovarian-peripheral vein gradient. Unexpectedly, the levels of androstenedione in the ovarian vein were normal, suggesting an alteration in the ovarian biosynthetic pathway for the production of T. Similar findings have been observed in hirsute women with hyperthecosis ovarii. After surgery, the peripheral vein levels of 17-OHP and T returned to normal, pointing toward the ovary as their source of excess. The data indicate that stromal luteinization of the massive ovarian edema may lead to changes in normal ovarian steroidogenesis that would be responsible for the clinical manifestations of this disorder.