In this study we investigated T-cell subsets, HLA-DR and IL2 receptor (IL2R, CD25) expression on T-cells in peripheral blood lymphocytes from the patients with childhood acute leukemia undergoing maintenance chemotherapy with 6-MP and MTX, and compared them with those in the healthy controls. There were decrease of relative number of CD4 positive (CD4+) cells and the increase of relative number of CD8 positive (CD8+) cells in comparison with those in controls; thus the ratio of CD4+ cells to CD 8+ cells decreased. HLA-DR and IL2R expression on T-cells increased in the patients. Increased HLA-DR expression was detected on both CD4+ cells and CD8+ cells, but the increased IL2R expression was related only to CD4+ cells. IL2R expression in the patients with side effects was higher than in controls. Methotrexate (MTX)-induced increase of HLA-DR and IL2R expression was observed in 2 of every 3 patients undergoing intensive chemotherapy.