Purpose of investigation: The role of progestogens in the genesis of ovarian cancer remains unclear although a rather protective behaviour has been suggested. Epidemiological studies indicate a possible increase in the risk for combined estrogen/progestin as compared to estrogen alone. It is ambigious whether a difference exists within the various progestogens. Apart from sex steroids, growth factors play a crucial role in the genesis of ovarian cancer, although as yet little investigated. In the present study we have explored the effect of progesterone (P), medroxyprogesterone acetate (MPA) and norethisterone (NET) on the proliferation of human ovarian cancer cells alone and in the presence of growth factors. Methods: For the experiments human ovarian cancer cells (OVCAR-3) were used. The progestogens were tested at the concen­trations of 0.01 to 10 µM. The growth factor mixture consisted of EGF, FGF und IGF-1, each at a concentration of 10 pM. The incu­bation time was three or seven days. Proliferation rate was measured by an ATP-assay. Results: After three days'incubation the growth factors induced an increase in the proliferation rate of about 50%. Progesterone alone did not show any significant change as compared to the control values, whereas NET and MPA elicited a significant increase at I and 10 µM and at 1 µM, respectively. In the presence of growth factors none of the progestogens was able to inhibit the pro­liferative stimulation. After seven days' incubation the growth factors still showed an increase of about 50%. MPA alone had an inhibitory effect at 10 µM, for NET and P no effects were observed. Again in the presence of growth factors no progestogen was able to show an inhibitory effect. Conclusion: Our results indicate that progestogens do not have a protective role on the growth of pre-existing ovarian cancer cells, at least in the presence of growth factors. Further investigations are worthwile to evaluate possible differences between the effect of the various progestogens.