Lysates of erythrocytes and sera of 52 patients with osteoarthrosis (OA) and 30 healthy subjects were used used to determine adenosine deaminidase (ADA, AMP deaminase (AMPDA) and adenine deaminidase (AD). Their activities were unrelated to the age and sex of the patients. At admission, patients with OA showed enhanced activity of ADA in sera and reduced activity of AMPDA and AD in lysates compared with normal values. These changes depended on clinical features of OA and were especially pronounced in patients with poly-OA and synovitis. These data suggest participation of enzymes of the adenyl branch of purine metabolism in pathogenesis of OA. Treatment of hospitalized patients allowed to achieve positive dynamics of the above activities coupled to their improved clinical conditions even though enzymatic activity of erythrocyte lysates remained different from that in healthy subjects. It is concluded that enzymatic assays used in the study may be used as additional diagnostic methods for the assessment of synovitis and optimizatic of control over efficiency of OA therapy.