To determine the CD 30 expression on peripheral blood T lymphocyte subsets in patients with hemorrhagic fever with renal syndrome (HFRS) and its clinical implications, double immunofluorescence technique and flow cytometry were used. There was no significant difference among the severe group, mild-moderate group and normal control group in the CD + 4CD - 30 T lymphocyte subset. While the CD + 4CD + 30 T cells of HFRS patients were increased and the difference between severe group and mild-moderate group or normal control group were very significant (P<0.01) and the difference between the mild-moderate group and normal control group was also significant (P<0.05). The CD + 8CD - 30 T cells were increased while the CD + 8CD + 30 T cells decreased obviously in HFRS patients, and the differences among three groups in both subsets were very significant (P<0.01). The results showed that the humoral immunity and cellular immunity are overactive in HFRS patients during acute phase. The loss of balance between T lymphocyte subsets may play an important role in the pathophysiology of HFRS and is closely correlated with the severity of the HFRS. To determine the CD 30 expression on peripheral blood T lymphocyte subsets in patients with hemorrhagic fever with renal syndrome (HFRS) and its clinical implications, double immunofluorescence technique and flow cytometry were used. There was no significant difference among the severe group, mild-moderate while the CD + 4CD + 30 T cells of HFRS patients were increased and the difference between severe groups and mild-moderate group or normal control groups were very significant (P <0.01) and the difference between the mild-moderate group and normal control group was also significant (P <0.05). The CD + 8CD - 30 T cells were increased while the CD + 8CD + 30 T cells decreased obviously in HFRS patients, and the differences among three groups in both subsets were very significant (P <0.01). The results showed that the humoral immunity and cellular immunity are overactive in HFRS pat loss during acute phase. The loss of balance between T lymphocyte subsets may play an important role in the pathophysiology of HFRS and is closely linked with the severity of the HFRS.