The blood serum of 57 women with uncomplicated pregnancies was quantitatively bioassayed for chorionic gonadotropin using a modification of the male frog pregnancy test. Several abnormalities of gestation with high serum gonadotropin titers were also assayed. These included chorionepithelioma, ectopic pregnancy, enzygotic twins, hydatidiform mole and eclampsia. All observations were reported as International Units of chorionic gonadotropin per cc. of serum. Serial serum titrations of chorionic gonadotropin were made in one patient with chorionepithelioma who was receiving stilbestrol and testosterone therapy. No apparent beneficial effect on the gonadotropin titers or the climical course of the disease was noted. The seasonal variation of the male Rana pipiens to chorionic gonadotropin was discussed. The frog responds (with gametokinesis) to lesser amounts of chorionic gonadotropin in the spring. The least sensitivity was encountered in the late summer.