Objective:To study the evalution of T lymphocyte in Severe Acute Respiratory Syndrome (SARS) patients.Methods:T lymphocyte in the peripheral blood was determined by Flow Cytometry in 53 patients with SARS. Results:The CD4 +T cell and CD8 +T cell decreased reversiblly in the cured SARS patients, but decreased progressively in the dead cases. The level and duration of the decrease are correlated with the patient's condition. The lowest CD4 +T cell count is 305?150 cells/?l(P