This paper reported the effect of Ma-Xin-Shi-Gan tang (Decoction of Herba Ephedrae, Semen Armeniacae Amarum, Radix Glycyrrhizae and Gypsum Fibrosum) on the immune function of the children with acute lower respiratory tract infection (ALRTI). 64 cases of ALRTI children were chosen for clinical observation. Laboratory researches including 7 immune indexes: blood OKT3+ cell, OKT4+ cell, OKT8+ cell and OKT4+/OKT8+ cell ratio, serum IgG, IgA, IgM. Some tests in experimental mice were also made. The results showed: (1) Before treatment, the blood OKT3+ cell, OKT4+ cell and OKT4+/OKT8+ cell ratio of the ALRTI children were lower, OKT8+ cell was higher than that of the normal group, which indicated lowered function of cell mediated immunity (CMI) in ALRTI children. Furthermore, IgM content in serum of the ALRTI children was significantly higher than that of the normal group, which indicated a hyperhumoral immunity (HI). (2) Blood OKT4+ cell and OKT4+/OKT8+ cell ratio in children after treatment with the Decoction were higher than those before treatment, which suggested the Decoction can regulate the cell ratio of OKT4+ and OKT8+, and relieve the functional inhibition of CMI in ALRTI children, while comparing with the western medicine (WM) group, the blood OKT3+ cell, OKT4+ cell and serum IgG content in the Decoction group after treatment were higher. In the WM group, the serum IgG and IgA contents were lower than those of the normal group, which indicated inhibited function of HI after treatment. (3) In experimental mice, the Decoction can increase the phagocytic index of the macrophage, the spleen index and the level of serum hemolysin. It can also enhance the skin delayed allergic reaction of the mice.(ABSTRACT TRUNCATED AT 250 WORDS)