The aim of this study was to estimate HCG and its free subunits (alpha and beta) content in placental tissue and to determine the characteristic pattern of their ratio changes in the course of normal pregnancy. For this we used 47 samples of placental extracts. The tissue was extracted and gel filtrated on a calibrated Sephadex-G-100 column. Crude placental extracts and each fraction after chromatography were radioimmunoassayed for HCG, alpha HCG and beta HCG in a double antibody, homologous radioimmunoassay system. We obtained the following results: Peak of native HCG secretion occurred in 6-8 gestational week thereafter its concentration in placenta decreases. The absolute amount of free alpha HCG increased after the first trimester like to native HCG, but the relative quantity of alpha HCG exceeded that for HCG. In extracts from mature placenta quantity of free alpha HCG was about 5-10-fold more than HCG. In chorionic extracts from the first trimester we have proved the free beta subunit of HCG. It has not been found in extracts from mature placenta.