By performing the bone-marrow tissue culture of normal person and patients with anchylostomiasis with addition of the filtrate from fresh emulsion of hookworms, the author obtained the following results: 1. Bone-marrow tissue culture of normal person: Even when the bone marrow tissue is cultured in the serum of normal person with addition of the filtrate or emulsion of hook-worms, eosinohils in the growth zone do not increase, but when the bone marrow is cultured in the serum of the anchylostomiasis with addition of the filtrate, eosinophilia is induced, and at the same time the wandering velocity of eosinophils is accelerated. 2. Bone-marrow tissue culture of anchylostomiasis: In the bone marrow tissue culture with addition of the above mentioned filtrate irrespective of kind of serum used, eosinophils in the growth zone increase markedly in all (especially markedly in the case using patient's serum). From these, it is believed that the serum and bone marrow of the patient contain antibody to hookworm, and when bone marrow is cultured with addition of the filtrate of hookworm emulsion, eosinophilia and acceleration of motility of eosinophils are induced in all as the result of the antigen-antibody reaction. In other words, it seems that allergic reaction plays an important role in inducing eosinophilia of anchylostomiasis.