The formation of an ischemic focus in the myocardium is paralleled by autoimmune processes involving immunoglobulins with abnormal thermal solubility, cryoglobulins. Serum levels of cryoglobulins and their complexes were measured in 25 patients with Q-forming myocardial infarction on days 1, 2, 3, 7, and 14 of the disease. Cryoprotein levels were measured by spectrophotometry, concentrations of IgM, IgA, IgG, and fibronectin by ELISA. Cryocomplexes in patients with myocardial infarction consist of polyclonal immunoglobulins of the main classes IgG and IgM, less often IgA, while cryoglobulinemia in this patient population is referred to type III according to the commonly used classification by Brouet. Fibronectin was detected in the cryocomplexes throughout the entire period of observation, its dynamics being opposite to that of the cryocomplexes level.