The article is devoted to the role of homocysteine in the human body. Amino acid homocysteine is the product of demethylation of methionine. The accumulation of homocysteine leads to the relaxation of the walls of the arteries, the appearance of local defects in the endothelium, which in turn leads to the deposition of cholesterol and calcium into the vascular wall. As a result of the disturbed metabolism of homocysteine, it damages the vascular system of the basmia, which can lead to irreversible ischemic brain damage.