Relevance. Periprosthetic infection is one of the most difficult health problems. Objective — to assess the concentration of vancomycin on days 1, 3 and 7 in serum and periarticular fluid in patients with periprosthetic infection of the knee joint after installing an articulating spacer with an antibiotic against the background of intravenous antibacterial therapy. Material and methods. The concentration of vancomycin was studied by the method of immunochemiluminescent analysis in serum and periarticular fluid from the joints at a minimum concentration at 1, 3 and 7 days after surgery in 9 patients (group I) with intravenous administration of vancomycin and using a spacer with vancomycin, 8 patients with intravenous administration of another antibiotic (group II). Results. In group I, the average concentration of vancomycin in serum on day 1 after surgery was close to the therapeutic 16.8 μg/ml [9.8; 16.9], on days 3 and 7 it was respectively 20.18 μg/ml [16.6; 22.69] and 16.43 μg/ml [13.2; 27.3]. In the periarticular fluid on days 1 and 3, high concentrations of vancomycin were found: 59.84 μg/ml [57.3; 74.0] and 43.0 μg/ml [36.53; 31.2], respectively, decreasing by 7 days to 29.94 µg/ml [21.44; 36.5], but significantly exceeding the minimum inhibitory concentration of isolated pathogens. In group II, low serum vancomycin concentrations of 2.86 µg/ml [1.23; 3.9] were detected in patients’ serum on days 1, 3, and 7; 3.05 µg/ml [1.25; 4.25]; 3.14 µg/ml [2.16; 3.47]. In the paraarticular fluid, on the 1st, 3rd day, the concentrations of vancomycin on the other hand were high 52.95 µg/ml [20.4; 60.4]; 31.36 µg/ml [22.6; 36.5]; but with a gradual decrease to 7 days 11.09 µg/ml [8.69; 17.15]. A significant difference in the concentrations of vancomycin in the periarticular fluid in patients of groups I and II was obtained only on day 7 after surgery (Uemp=7) with p<0.01. Conclusion. The use of vancomycin in the composition of the cement allows achieving concentrations of vancomycin, significantly higher than the minimum inhibitory concentration for the most common gram-positive pathogens of periprosthetic infection. The combination of intravenous and local therapy with vancomycin yields higher concentrations for a longer period.