Sera from 181 patients, 37 of' which suffered from trophoblastic tumors (hydatidiform mole, destructive hydatidifbrm mole, and chorioepithelioma of' the uterus), I00 patients-with other ,forms of tumors and 43 patients with various gynecological diseases, were studied with the use of an immunological test for the detection of' beta,globulin of "pregnancy zone ". In the control group there were 106 serum samples of women at different stages of pregnancy and 257 samples of normal adults (165 women and 92 men). Thus, 544 serum samples from patients and from normal adults were studied. The immunochemical test for the beta,-globulin was positive in patients with trophoblastic tumors before surgical removal or before chemotherapy. A.fter surgery andlor complete course of' chemotherapy, the test for beta,-globulin became, as u rule,negative. This globulin is detected also in normal pregnancy serum. I t is supposed that the beta,-globulin of'" pregnancy zone '' is synthetized in the placenta and is released in the circulation of women during normal pregnancy; also it is produced by cells of trophoblastic tumors. The diagnostic and prognostic signijicance of the immunochemical test for the " pregnancy zone '' beta,-globulin in trophoblastic tumors is discussed.