To Study T lymphocyte subsets, including T(H1) and T(H2) cells in peripheral blood mononuclear cells (PBMC) of children with mycoplasma pneumonia, understand immunopathogenesis and explore the possibility of immunotherapy of patients with mycoplasma pneumonia.Fresh peripheral blood samples of patients from two groups, group 1, mycoplasma pneumonia (MP) group (35 cases, 15 males and 20 females, age range 3 - 13 years, mean 9 years), and control group consisted of 28 healthy children (14 males and 14 females, age range 3 - 12 years, mean 7 years) were treated and run through the flow cytometry. The data were obtained by using Simultest IMK-Lymphocyte software and the percentage of CD(3)(+), CD(3)(+)CD(4)(+), CD(3)(+)CD(8)(+), CD(3)(-)CD(19)(+) and CD(3)(-)CD(16 + 56)(+) cells were counted. The percentage of T(H1) and T(H2) cells were gained through determination of intracellular cytokines IFN-gamma or IL-4 in CD(4)(+) cells by flow cytometry. The 35 patients with MP were hospitalized at our hospital. In addition to fever and cough, all the patents had abnormal X-ray findings and/or moist rale on auscultation of the lungs. The IgM antibody to Mycoplasma pneumoniae was positive in each patient. Immunoglobulins were measured, and PPD skin tests were performed in 30 out of the 35 patients with MP. T test and rank sum test by SPSS FOR WINDOWS 10.0 was used for statistical analysis.The percentage of CD(3)(+) and CD(4)(+) T lymphocyte was 68.00 +/- 6.66 and 37.86 +/- 5.84, respectively, in MP group, and 63.71 +/- 7.92 and 34.54 +/- 6.23 in control group (P < 0.05). The percentage of T(H1) cells was 14.13 +/- 8.46 in patients and 20.77 +/- 6.89 in normal control group (P = 0.001). The percentage of NK cells was 15.57 +/- 12.16 and 20.39 +/- 9.64 in MP and control group (P < 0.01). The ratio of T(H1)/T(H2) in MP group was lower than that in control group (P < 0.05). However the percentage of CD(8), T(H2), B cells and CD(4)/CD(8) had no difference between the MP and control groups. The levels of IgG, IgA, and IgM in serum were normal in most of patients except for a few patients who had elevated IgA and IgM levels. The PPD skin tests were negative in 30 out of 35 patients.In this study a higher percentage of CD(3)(+), CD(4)(+) T lymphocyte and lower percentage of T(H1), NK cells in PBMC of patients with mycoplasma pneumonia were found. The ratio of T(H1) and T(H2) cells in patients was also lower. None of thirty patients had positive PPD skin tests. Unbalanced cell-mediated immunity with a tendency toward T(H2) existed in patients with MP. Therefore, immunomodulators may be useful in treatment of mycoplasma pneumonia.