The aim of this study was to determine prognostic markers for the outcome after 36 months of therapy with disease-modifying anti-rheumatic drugs (DMARDs) in patients with rheumatoid arthritis (RA) and to study serial cytokine serum levels. During 36 months, 20 patients receiving DMARDs (nine patients gold sodium thiomalate and 11 patients methotrexate, no comparison undertaken) were followed for clinical and laboratory data. Investigation at baseline, 12, 24 and 36 months, included clinical, radiological and laboratory parameters such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and interleukin (IL)-1 beta, IL-6, tumor necrosis factor alpha (TNF-alpha), IL-1 receptor antagonist (IL-1RA) and IL-2. During the 3 yr of therapy, the patients showed significant clinical improvement and decline of ESR, CRP, and serum levels of IL-6 and IL-2. The decrease in IL-6 serum levels during the first year of therapy correlated significantly with the decrease, after 36 months, in the number of inflamed joints (r = 0.7608, P < 0.005), Lansbury index (r = 0.6642, P < 0.005) and morning stiffness (r = -0.6561, P < 0.005). In contrast to IL-6 or IL-2, TNF-alpha and IL-1RA did not vary significantly during the 3 yr of therapy. During 36 months of therapy, patients treated with DMARD showed significant improvement of clinical parameters and a trend for delayed progression of radiographic damage. The decrease in IL-6 concentration in serum during the first 12 months was the best prognostic marker for the clinical outcome after 36 months of DMARD therapy.