Four fractions were isolated from extracts of ischemized and control liver tissues. Toxic activity of the fractions did not depend on the content of proteins. Distinct immunogeneity and high antigenic activity of the ischemized liver tissue were noted. As shown by electron microscopy the fractions consisted of mitochondria destructed by various degree. The data obtained suggest the polypeptide structure of the toxic factor. Molecular weight of the active component was about 10000-20000 daltons.