Rheumatoid arthritis (RA) is a chronic autoimmune disease with a prevelance of around 1% in the world. Characterized by joint swelling, joint tenderness, and synovial hyperplasia, inflammatory process eventually leads to cartilage and bone destruction, severe disability and premature mortality. Differencial diagnosis is based on multiple diagnostic methods, including laboratory tests, radiography or other imaging techniques. Along with specific inflammatory markers such as CRP or ESR, laboratory tests include specific antibodies (anti-CCP) for RA diagnostics. Although total WBC count with cell population data gives a valuable information about disease activity, VCS technology gives information about each individua) leukocyte cell population therefore giving biochemists a new insight to the pathology of inflammatory process. In this masters thesis, the VCS parameters mean lymphocyte volume (MCV Ly) and mean monocyte volume (MCV Mo) acquired from a Beckman Coulter DxH800 haematology analyzer were investigated to determine which of them could indicate the activation of inflammatory process in RA. Total number of samples was 140 in the test group and 32 in control group. Out of 140 samples, 34 were patients with active rheumatoid arthritis and 104 were in remission. The results are as follows: MCV Ly is significantly increased in patients with RA compared with control group as well as in patients with active RA compared with those i11 remission. MCV Mo is also sig11ificantly increased in patients RA compared with control group as well as in patients with active RA compared with those in remission. There is a positive correlation between MCV Ly a11d MCV Mo and CRP and DAS28 in active rheumatoid arthritis. MCV Ly a11d MCV Mo are also significantly increased in patients on anti-TNF-a: with patients on anti-IL-6 drugs. These results indicate that MCV Ly and MCV Mo may have potential for use in RA, monitoring disease activity as well as efficacy of therapy.