Proliferating tumor cells obtained from ovarian, mammary, and endometrial tumors in tissue culture were tested for the influence of proteohormones and steroid hormones on cellular DNA synthesis and cell growth. The gonadotropic hormones stimulated DNA synthesis of ovarian tumor cells by single administration, or in combination with cortisol, up to the 11-fold of the comparable controls. The hormone sensitivity of the cell lines was variable, resulting in individual reaction patterns. There was no correlation to the histological diagnosis of the primary tumors with respect to the grade of differentiation. The results suggest that ovarian tumor cells in tissue culture can maintain sensitivity to organotropic hormones. Compared to the ovarian carcinoma lines, mammary or endometrial tumor cells did not respond to a similar extent. Progesterone decreased DNA synthesis of endometrial carcinoma cells.