Having investigated about those receptor substances contained in a chick erythrocytes that were used in hemagglutination reaction by both Okayama 52 A strain as well as Okayama 52 B strain of Japanese B encephalitis virus, obtained the following results. 1) There are contained mach receptor substances in a chick erythrocytes immediately after having been hatched; however, as they grew up, indicated a decrease at 11-14 days, reducing itself to below 10%. 2) likewise, in a chick serum immediately after hatching, various kinds of inhibiting substances may be found out, due to an inhibition test, but they indicate a marked decrease at about 8-11 days, coming down below 10%. From this fact, it, is considered that these two factors have the same or very closely resembled properties. 3) In case we have fixed certain blood preparation specimens by dint of melthanol-formalin 9 : 1 solution and have stained it with Victorian blau, the erythrocytes are apt to be stained deep within one week of hatching, leaving some lipo-protein, non-stainable grobules around those erythrocytes. Thew grobules indicate nothing but lipo-protein contained in plasmas, which bear a close relation to any inhibition-test. 4) Because in case we have inoculated a rabbit with the serum of chick just has been hatched, which contained a great deal of lipo-protein, there would be produced agglutinin that reacts well to chick erythrocytes; this lipo-protein has been taken for a substance quite the same or closely akin to agglutinin receptor substance of chick erythrocytes. 5) If an inhibition test should be carried out by cholesterin and lecithin, the former acts on antigens, which results in depriving the reactions power of erythrocytes toward receptor. From this, it has come to pass that the behavior of cholesterin as inhibition substance as well as receptor substance bears a great significance.