The kinetics of cytokine mRNA expression was studied in porcine alveolar macrophages using an RT-PCR assay. The expression levels of IFN- gamma, IL-2, IL-4, IL-6, GM-CSF, IL-12 p35, and IL-12 p40 were examined after 2, 4, 14, 24, 48, and 72 h of incubation in unstimulated control and LPS-stimulated cells. The expression contents of IFN-gamma, IL-2, and IL-4 were not detected in both unstimulated and LPS-stimulated cells. On the other hand, the expression levels of IL-6, GM-CSF, and IL-12 in LPS-stimulated cells were almost always higher than those in control cells. Among those cytokines, IL-6 exhibited the predominant expression, and GM-CSF, IL-12 p40, and IL-12 p35 followed in the descending order. The times to reach the peak expression levels for IL-6, and GM-CSF, IL-12 p35, and IL-12 p40 were 14, and 24 h, respectively. After reaching the peak expression point, the expression levels of IL-6, GM-CSF, and IL-12 p40 reduced to the baseline by 72 h after stimulation, however, IL-12 p35 still kept a substantial expression by the same time. This study demonstrates that porcine alveolar macrophages primarily respond to express IL-6, GM-CSF, and IL-12 by LPS-stimulation and have a cytokine-specific expression profile during the stimulation time.