The authors deal with the value of the avidin-biotin enzyme immunoassay (A-B-Elisa) which was introduced by them for the demonstration of human chorion gonadotropin beta subunit (HCG-b). It is pointed out that the possibility of the diagnosis of extrauterine pregnancy improved significantly by measuring the HCG-b level with A-B-ELISA method. The HCG-b hormone level over 5 mIU/ml refers to trophoblast activity and it is absolutely necessary to observe the patients in this case. In cases where the HCG-b level is low and the clinical symptoms are uncertain the patient must be kept under close observation and serial serum samples must be examined. Significant rise of HCG-b level refers to normal intrauterine pregnancy whereas a slightly rising, or unchanging or even decreasing hormone level suggest the possibility of extrauterine gravidity.