The protective action of live avirulent vaccine against bovine trichophytosis, produced by the Bioveta National Corporation at Ivanovice na Hané, was very good and fully comparable with the earlier vaccine produced from the virulent live culture of Trichophyton verrucosum. Experimental challenge with a massive dose of a virulent strain of T. verrucosum produced only minor surface dermal changes in the calves vaccinated with these vaccines, but these changes spontaneously disappeared in a short time. In the control non-vaccinated calves, large and deep lesions were induced by the challenge, spreading to the neighbouring tissues. Compared with both live biopreparations, the protective effect of inactivated vaccine prepared by the irradiation of virulent vaccine with Co60 was much lower.