We developed a new immunological method of determinating urinary HCG (Human Chorionic Gonadotropin), in which antigen-antibody reaction is allowed to proceed while HCG is being adsorbed to kaolin particles. With this method, we conducted some immunological studies with normal and abnormal pregnancies, and obtained the results as follows. 1. The urinary HCG concentration in normal pregnancies began to increase by about 7 gestational weeks, which reached its maximum at 12 weeks, thereafter it decrease gradually. 2. In the cases of abortus imminens the urinary HCG concentration was somewhat over than that in normal pregnancy, but in those cases whose prognosis was poor, HCG concentration was markedly low. 3. In the cases of hydatidiform mole the urinary HCG concentration was found to be abnormally high in two cases out of three, but it became negative (500iu/l) by 23 to 40 postoperative days. 4. As to the correlation between Friedman's reaction and our determination method we found the correlation quotient to be 0.583, indicating a moderate correlation. 5. The threshold of Friedman's reaction was found to be within 7.5 to 10.0iu.