Liu-Wei-Di-Huang Wan (LWDHW) has been used by traditional Chinese doctors to treat asthma patients. This study was to examine the potential effect of this decoction on the regulation of T helper (Th)1- and Th2-type cytokine gene expression in vitro. Peripheral blood mononuclear cells (PBMC) were activated with mitogen for 24 hours in the presence or absence of LWDHW extracts. Concentrations of different cytokines in the culture supernatants were determined with ELISA. RNA isolated from cultured cells was subjected to RT-PCR analysis. The results showed that the expression of all cytokines (Th2-type: IL-4, IL-5, IL-10, or IL-13 and Th1-type: IL-2 and IFN-gamma) examined was inhibited at both RNA and protein levels by LWDHW. Since the cell viability was similar in all cultures, the reduction of cytokine production was not due to the toxicity of LWDHW. Moreover, the cells either retained or increased their capacity to respond to mitogen stimulation after incubation with the LWDHW decoction. Therefore, the data suggest that LWDHW functioned directly on cytokine gene expression from activated PBMC.