A comprehensive study of the intensity of free radical oxydation of lipids, of changes in the total polyunsaturated free acids and antiradical activity of the blood lipids undertaken in 73 patients with different forms of ischaemic heart disease showed that in all forms of illness there exists intensification of peroxyde oxydation of lipids, more marked in acute myocardial infarction. Rise of antiradical activity of lipids is a sequel to activation of the compensatory mechanisms, directed at neutralization of the negative action of toxic lipid peroxydes. Correlation between the changes in the total polyunsaturated fatty acids and antiradical activity of the lipids permits one to consider that accumulation of polyene acids may be one of the factors helping the intensification of free radical processes.