The aim of our study was to evaluate the changes in T (CD3), B(CD19) lymphocytes, CD4 and CD8 subsets, activated CD3+ HLA-DR+ lymphocytes, lymphocytes with receptor for IL-2 (CD3+CD25), NK cells as well as the rate of CD4/CD8 in 30 patients with recognized Lyme disease, before and after antibiotic therapy. Patients were divided into the following groups: Group I n = 9--without detected specific antibodies against B. burgdorferi and with clinical recognition of EM(erythema migrans). Group II n = 10--with increased IgM production, with a clinical form of Lyme arthritis and neuroborreliosis. Group III n = 11--with increased IgG anti B. burgdorferi production, with clinical recognition of Lyme arthritis. The results were compared with the results obtained in the control group consisting of 90 healthy people. The measurements were performed in the flow cytometer COULTER EPI XL with Becton Dickinson antibodies. The antibodies against B. burgdorferi were detected by means of ELISA method using Dako, Biomedica and Biocom kits. The statistic analysis was performed with AnStat Program. The changes in lymphocyte subsets were characterised by the decrease in the percentage of CD4, CD8, NK and CD3+HLA-DR+ lymphocytes in peripheral blood before treatment with later tendency to increase. The results show that the lag phase of antibodies production coincides with high activity of lymphocytes (group I). The significant level of antibodies in IgM class induced by the collaboration of T and B cells was found in the group II. In the group III, in which antibodies in IgG class predominated, the changes in lymphocyte subsets were less intensive. The results of our investigations indicate that the immune response in Lyme disease develops mainly with the participation of both cellular and humoral response which is involved in both the defense against and the pathogenesis of the disease.