OBJECTIVE: To explore the determination of tumor necrosis factor-α(TNF-α) in the systemic inflammatory response syndrome(SIRS) caused by pneumonia in children. METHODS: Fifty-one children with pneumonia were divided into the SIRS group(n=36) and non-SIRS group(n=15) according to the entry criteria of childh ood SIRS. The SIRS group was subdivided into the S1 group(n=28) and S2 grou p(n=8) according to disease severity criteria(S1 having 2 SIRS entry criteria items and S2 having 3 items). TNF-α levels were then determined in each group.RESULTS: On day 1, the TNF-α level in the SIRS group [(26.05±18.27)ng/L] was higher than that in the non-SIRS group [(9.54±4.33)ng/L](P<0.05). On days 1, 3 and 5 of ho spitalization, the TNF-α level of the S2 group was higher than that of S1 group [(39.38±21.91) ng/L vs(22.24±15.51) ng/L,(41.63±20.22) ng/L vs(26.22±18.79)ng/L and(45.58±17.19)ng/L vs(23.21±15.91)ng/L, respectively; all P < 0.05]; m oreover it appeared to elevate constantly. CONCLUSIONS: TNF-α may be of value in assessing the degree of severity and prognosis of SIRS caused by pneumonia.