An attempts was made at evaluation of the changes of acute phase proteins-seromucoid (BRS), alpha 1-acid glycoprotein (alpha 1-AGP), alpha 1-antitrypsin (alpha 1-AT), haptoglobin (Hp), C3 protein of complement system (C3), C1 esterase inhibitor (C1-INH), and transferrin (Tf) in the serum of children with rheumatoid arthritis. The patients were divided into clinical and age groups. The studies carried out have shown in ill children increase of BRS, alpha 1-AGP, alpha 1-AT, Hp, and C1-INH levels, During remission increased levels of alpha 1-AGP and Hp persisted. In the studied clinical groups a positive correlation was found between the intensity of changes of the studied indices and the degree of disease activity. In the age groups greater increase of the levels of the studied acute phase proteins was found in the group of preschool children and the group of puberty spurt. The obtained results suggest that the determination of acute phase proteins may be useful in laboratory investigation of children with rheumatoid arthritis.