Cell mediated as well as humoral immune response was evaluated in 14 lyme arthritis patients. Significant decrease of T cells percentage was observed in comparison to normal values. It was related particularly to CD4+ subset and resulted in significant decrease of CD4+/CD8+ ratio. Statistically significant increase of B cells percentage was accompanied by elevated concentrations of immunoglobulin M, complement components C3 and C4. Immunoglobulins A and G, as well as circulating immune complexes remained on the normal level. These results indicate suppression of cellular and activation of humoral immune response in patients with Lyme arthritis.