For the immunologic determination of H.C.G. in the patients of hyperemesis gravidarum and evaluation of its titer, basic experiments and semi-quantitative assay had been performed by means of hemagglutination inhibition technique and the obstained results were as following. 1. For the immunization of rabbits, relatively high purity of H.C.G.(5,427IU/mg)was used as antigen and through the effect of additional booster injection of antigen and complete Freund`s adjuvant, high titer of antiserum was obstained. 2. For the evaluation of the specificity of obstained antiserum, weighing technique of immature rat ovary and Ouchterlony method was appllied. The results showed that the used H.C.G. was relatively pure. 3. In the observed patients, primipara occupied 56.7% and the age ranged 22~37, the majority (66.7%) being in 20~30 years range. 4. In Hyperemesis Gravidarum, the titer of H.C.G. in serum and urine were significantly higher than that of normal pregnancy at the same period expect the urinary finding in 11~12wks. 5. The severity of emetic symptoms seemed not exactly correlate with the titer of H.C.G.