Objective:To study the correlation between the effects of oxygen free radicals (OFR) with T cell subsets on pathogenesis of hemorrhagic fever with syndrome(HFRS).Methods:Serum levels of SOD and MDA.T cell subsets in 54 patients with HFRS were sequentially investigate and correlation. Results:The level of serum SOD in febrile phase was lower than that of normal control.The level of serum MDA in febrile phase was higher than that of normal group;the sum of CD4 + cell in febrile phase was signficantly lower than that normal group,CD8 + cell was significantly higher than that of control group,and its changes must severe in oliguric phase.The resuts also showed that there was sum correlation existed between MDA and T cell subsets.Conclusion:These findings demonstrated that irregulating immunity of HFRS patients was correlation with OFR.