[en] The changes in pathogenicity and toxin producing capacity by radiation exposure were investigated with Vero toxin producing E coli O157 and mycotoxin producing eumycetes including A. flavus, A. parasiticus and A. ochraceus and A. usamii. Each cell suspension was exposed to γ-ray (⁶⁰Co, 150 kCi) at 0-2.0 kGy and an aliquot of the suspension was cultured on agar plate for counting the living cell number. The producing ability of Vero toxin was determined according to reverse passive latex agglutination. Analysis of aflatoxin and ochratoxin were performed using HPLC. It was demonstrated that E.coli O157:H7 could be sterilized by γ-ray exposed at a lower dose than that of ordinary strain of E.coli and Vero toxin producing ability were higher in the cells exposed to 0.1 kGy than non-exposed cells. In addition, the aflatoxin productions of A. flavus and A. parasiticus were slightly increased by γ-ray exposure at a low dose, whereas A. ochraceus showed comparatively higher resistance to γ-ray exposure, but its producing ability for ochratoxin A was reduced and the producing ability of A. usamii was slightly increased. (M.N.)