OBJECTIVE: To study the immune function of T-lymphocyte and erythrocyte in the peripheral blood of children with febrile convulsion. METHODS: Eighty two children with typical febrile convulsion, 40 children with acute upper respiratory tract infection (URI) and 40 normal children were enrolled. The proliferation reaction of T-lymphocyte to PHA, distribution of T-lymphocyte phenotype subsets, expression of activation markers CD25 (IL-2R) and HLA-DR, and level of γ-interferon induced by PHA were assayed. Erythrocyte immune function was simultaneously measured by rosette formation rates of RBC-C3bR and RBC-IC. RESULTS: The counts per minute (CPM) and stimulation index (SI), the measurements expressing T-lymphocyte proliferation assay in simple febrile convulsion (SFC) children, were 5 609.4±3 587.4 and 20.5±15.6, and 2 817.3±2 422.8 and 11.0±8.4 in complex febrile convulsion (CFC) children. They were significantly lower than those in the normal controls (20 305.9±12 810.3 and 69.2±45.2) and in the URI group (9 785.2±7 509.8 and 44.5±39.8) (P<0.05). The CD3, CD4 and CD4/CD8 ratio in the SFC children were (40.0±8.2)%, (26.1±9.0)% and 1.1±0.4 and (932.8±6.9)%, (17.8±4.9)% and 0.8±0.1 in the CFC children. They were all significantly lower than those in the normal controls ［(64.1±6.7)%, (47.7±5.5)% and 1.9±0.8］ and in the URI group ［(63.0±9.3), (42.4±8.2)% and 1.6±0.4］ (P<0.01). The expression rates of CD25 (IL-2R) and HLA-DR antigen in the spontaneous condition in the SFC children were (8.9±3.6)% and (16.2±5.6)% and (6.3±1.9)% and (12.4±3.4)% in the CFS children. They were lower than those in the normal controls ［(12.8±2.5)% and (20.2±5.2)%］and in the URI group ［(15.0±3.0)% and (20.5±2.8)%］ (P<0.01) and there were also differences in the SFC children and in the CFS children (P<0.05). After PHA induction, the expression rates of CD25 (IL-2R) and HLA-DR antigen in the SFC children were (57.0±5.1) and (57.8±6.0) and (53.0±12.0)% and (54.7±9.7)% in the CFC children. They were significantly lower than those in the normal controls ［(65.7±5.7)% and (68.8±6.2)%］ (P<0.05) and in the URI group ［(64.3±6.4)% and (67.1±8.6)%］(P<0.01). The γ-IFN level of PBMC induced by PHA in the SFC and CFC children ［(1.80±0.4) and (1.6±0.1) ng/ml］ was significantly lower than that in the normal controls ［(2.4±0.9) ng/ml］(P<0.05). No difference was found compared with the URI group. The rate of rosette formation of RBC-C3b in the SFC children was (9.1±4.9)% and it was significantly lower than that in the normal controls and the URI group ［(15.8±5.7)% and (13.5±5.1)%］(P<0.01), but there was no difference in the SFC children, the normal controls and the URI group. The rate of rosette formation of RBCIC in the SFC children and the CFC children ［(3.0±1.0) and (2.6±0.7)%］ was significantly lower than that in the normal controls ［(3.7±1.3)%］ and the URI group ［(3.9±1.4)%］(P<0.05). CONCLUSIONS: Both T-lymphocyte immune function and erythrocyte immune function in the children with FC were significantly impaired. The impair was more severe in the CFC children than that in the SFC children.