Blood eosinophils due to worm infestations can either decrease or increase in the first month following specific treatment, as we observsd in a sample of 57 children. In pinworm infestation, pin and hookworm infestation, hookworm infestation, trichuriasis with pin or liookworm infestation and in strangyloidiasis with hookworm infestation either increase or decrease of blood eosinophils can be expected during the first month after treatment, but decrease is uniform and Progressive in ali cases after the 2nd month. Now, blood eosinophils always descenãed vmmediately after treatment in our cases of strongyloidiasis, trichuriasis, and strongyloidiasis with ascariasis, while in cases of simultaneous infestation by three or four kinds of worms we could not see a uniform behavior of blood eosinophils after the treatment, but an irregular and delayed normalization of eosinophil count. It is important that the finding of a high blood eosinophil count in the first month after treatment of a worm-infestation does not necessarily mean failing in treatment.