Tested for toxicity were a total of 48 strains of pure cultures of the fungi: Aspergillus flavus, As. fumigatus, Penicillium, F. moniliforme, F. graminearum, Tr. lignorum. The methods of dermal tests, chick embryos, and feeding of young birds were employed. It was found that through dermal tests ten strains of the following species proved toxic: As. fumigatus, As. flavus, F. moniliforme, F. garminearum, and Trichoderma lignorum. Toxic for chick embryos were 13 strains of the same species. When young chickens were fed moulded silage toxic proved As. flavus and F. moniliforme. Chick embryos showed highest sensitivity to mycotoxins. The toxicity of the investigated strains varied depending on the methods employed, however, it was manifested to a different extent with all three methods.