Thermal injury is able to induce the immune functional inhibition in the host, but the mechanisms are largely unknown. The available evidence indicates that macrophages play an important role in immune regulations and host defenses. Thus, studies of the effect of thermal injury on macrophages are essential. Transcriptional factors of AP-1 (activator protein-1) and NF-кB (nuclear factor-кB) are critical members of signal transduction pathways. These transcriptional factors have been shown to be necessary for a variety of expressions of cytokine genes. In this investigation, the effect of thermal injury on AP-1 and NF-кB was studied using a model for the murine thermal injury. Our findings indicated that thermal injury mediated the inhibition of AP-1 and NF-кB DNA binding activities and c-fos and IL-12 p40 gene expressions in response to LPS.