OBJECTIVE: To study the changes of intracellular interleukin-6 (IL-6) and interferon-γ (IFN-γ) expressions in children with acute lymphoblastic leukemia (ALL) at different stages, and to examine the correlation between IL-6 and IFN-γ in ALL children. METHODS: The levels of intracellular IL-6 and IFN-γ in venous blood lymphocytes were detected by flow cytometry in 42 children with ALL at diagnosis and at remission stage. Twenty healthy children were used as the controls. RESULTS: The intracellular IL-6 level in ALL children at diagnosis was 81.74±9.31, which was much higher than that in the Control group (5.67±0.96 ) (P<0.01). The intracellular IFN-γ level in ALL children (1.31±0.32) was significantly lower than that in the Control group (1.46±0.49) (P<0.01). However, the intracellular IL-6 level (27.52±3.40) decreased remarkably in ALL patients at remission stage (P<0.01), but was still higher than that in the Control group (P<0.01). In contrast, the intracellular IFN-γ level (1.97±0.72) increased noticeably in ALL patients at remission stage, which was higher than that at diagnosis and the Control group (P<0.01). A negative correlation was found between the intracellular IL-6 and the IFN-γ levels in ALL patients (r=-0.476, P< 0.05). CONCLUSIONS: Intracellular IL-6 and IFN-γ levels may be used as the markers for monitoring the response to treatment in ALL patients. There is a negative correlation between intracellular IL-6 and IFN-γ levels in ALL children.