In 1979 and 1980, at the University Hospital Department of Gynecology and Obstetrics, 115 patients with extrauterine pregnancy were surgically treated. In 26 patients the value of the radioimmunologic determination of beta chorionic gonadotropin (HCG) in the serum was analysed. Along with it, also other clinicodiagnostic procedures (immunochemical test for pregnancy, culdocentesis, curettage) wire carried out. Not in a single case of extrauterine pregnancy in which the serum beta HCG level was determined, was the result falsely negative. The immunochemical test for pregnancy was falsely negative in 32.6% and the result of culdocentesis was falsely negative in 13.6% of the patients examined. In patients with negative culdocentesis laparoscopy was performed (10.4%), showing ectopic pregnancy. In the course of extrauterine pregnancy the elimination of beta HCG was significatly reduced in relation to its level in normal pregnancy. The concentration of beta HCG in the observed patients with extrauterine pregnancy ranged from 27 to 3924 IU/L. On the basis of a low beta HCG concentration in the serum it is possible to determine with much certainty that pregnancy is not quite normal. Of great help is the observation of changes in the elimination of this hormone over a short period of time. A timely diagnosis of extrauterine pregnancy improves prognosis of future fertility.