ln order to find out the regulatory function of hormone release of malignant choriocarcinoma, we cultured BeWo cell lines in vitro. The control was cultrued in cAMP and insulin free medium and for the experimental group, we add O. l, 0. 5 and l. 0 mM of cAMP , 1, 10 and. 20 uM of insulin and, 0. 1 mM and l uM, 0.5 mM and 10uM, and l.0 mM and 20 uM of cAMP and insulin (Group III), respectively to the medium, then cultured for 3 days in vitro. Release of B-hCG, estradiol and progesterone was measured by radioimmunoassay. In order to find out the effect of cAMP and insulin on cell proliferation, we measured the number of ceils by using hemocytometer after 3-day culture. The results were as follows. p-hCG release was increased in control and all experimental groups as prog~ressing the days of culture. Release of p-hCG was significantly inereased in proportion to the amount of cAMP and decreased in proportion to the amount of insulin as compared with those of control in all groups. In Group II1, inhibitory effeets of insulin was more predominant than cAWP of low concentration, and no inhibitory effect of insulin was found in the cases of stirnulatory effect, af high cancentration of cAMF in spite of high concentraion of insulin. 2. Estradiol release was relatively increased in control and Group II and Group III, but decreased in Group I with low concentration of eAMP as progressing the days of culture. In Group I and 11, release of estradiol was decreased as campared with that of control, In Group III, there was no statistical significance as compared, with control. 3. Progestterone release was rellatively increased in control and experimental graups as Progressing the days of culture. In Group I(except low concentration group), release of progesterone was increased on the 1st day of culture as compared with that of control. Howevere, in high cAMP concentration group, releee was decreased on the 2nd day of cuiture as compared with control. In Group III, there was a tendeney teward reduction of progesterone reiease as compared with control. 4. Number of cells was signifieantly inereased after 3-day culture. In Group l with high concentration of cAMP, number of cells was decrea.s, which suggested inhibition of cell proliferation. In Group II with high concetration of insulin, number of cells was increased, which suggested stimulatory effeet of insulin on cell proliferation. In Group III, neither stimulatory nor inhibitory effect was found. From the above results, it is thought that cAMF and insulin are related to synthesis and release of hCG and estrdiol in BeWo cell line whieh is one of malignant trophoblastic cell and are inaignificantly related to rele of progesterone as compared with B-hCG or estradiol. It was also found that cAMP inhibited and insulin stimulated BeWo cell proliferaition.