Antinuclear antibodies are a group of autoantibodies that react with various components of the nucleus. Determination of antibodies to nuclear antigens in serum is a test for systemic connective tissue diseases. The main goal of the study is to exclude SLE, since in this disease, ANA is detected in 95% of patients within 3 months after its onset. Definition of ANA is of great importance for the diagnosis of AIH connective tissue, the presence of these antibodies can be associated with SLE, RA, NWST, scleroderma, polymyositis, discoid lupus erythematosus, CREST syndrome, nodular periarteritis, dermatomyositis. With SLE, the antinuclear factor test has a high sensitivity (89%), but moderate specificity (78%), compared to the test for antibodies to native DNA (sensitivity - 38%, specificity 98%). Correlation between the height of the titer and the clinical condition of the patient is not present. Antinuclear antibodies are part of 11 criteria for diagnosing SLE of the American College of Rheumatism. The cell nucleus contains more than 100 different antigens (nucleic acids, histones, nuclear membrane proteins, spliceosome components, ribonucleoproteins, nucleolus proteins and centromeres, etc.). Ana can be divided into three groups: true ANA - to dsDNA, ssDNA, histones, nuclear RNA, AT to the extracted nuclear AG - to Sm, n-RNP , Scl 70, cytoplasmic AH - to SS-A (Ro) *, SS-B (La) * and Jo-1 . * SS-A (Ro) and SS-B (La) can be localized both in the cytoplasm and in the nuclei. A positive test result indicates that the patient has one or a combination of several varieties of ANA. A negative result of such a test in more than 95% of cases allows excluding SLE, lupus erythematosus (LBV), NOS, SZST, systemic sclerosis, DM and PM.