In the early stage of Mycobacterium tuberculosis infection, macrophages, in cooperation with interferon-gamma, a Th1 effector, are the first line of defense. Interleukin (IL)-4, a Th2 effector, is known to downregulate interferon-gamma. It is believed that the expression levels of IL-4 and its splicing variant-IL-4delta2 might be associated with Mycobacterium tuberculosis infection and chest radiographic patterns. The IL-4 and IL-4delta2 expressions in stimulated peripheral blood mononuclear cells of 76 tuberculosis patients, 48 pneumonic patients. and 36 healthy control subjects were evaluated by nested reverse transcriptase-polymerase chain reaction, and the expression of glyceraldehydes-3-phosphate dehydrogenase was used as an internal reference. The results showed that IL-4 mRNA expression was significantly decreased in patients with tuberculosis and nontubercular pneumonia compared with that in controls. The IL-4delta2 mRNA expression was positively correlated with IL-4 mRNA expression in all cases. The ratio of IL-4delta2 to IL-4 mRNA expression in tubercular patients with a cavity on chest radiography was significantly lower than that in patients without a chest cavity. In conclusion, the ratio of IL-4delta2 to IL-4 mRNA expression may play a key role in disease severity for patients with pulmonary tuberculosis. From our observations, the IL-4 mRNA expression efficiency was attenuated in patients with pulmonary infection, either tuberculosis or pneumonia.