Activated macrophages express inducible isoforms of nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), produce excessive amounts of nitric oxide (NO) and prostaglandin E(2) (PGE(2)), which play key roles in the processes of inflammation. Andrographis paniculata Nees is a traditional Chinese herb commonly used for treatment of infection, inflammation, and diarrhea. However, the mechanism of its therapeutic function is not well known. In the present study, the effect of neoandrographolide, one of bioactive components in A. paniculata, on iNOS-mediated NO production and COX-2-mediated PGE(2) in bacterial lipopolysaccharide (LPS) stimulated-murine macrophages was investigated. Neoandrographolide at concentrations (30-90 microM) significantly (p<0.05) inhibited the productions of NO and PGE(2) in LPS stimulated macrophages without inducing cytotoxicity. The effect of neoandrographolide also has been investigated on iNOS and COX-2 expression in activated macrophage by using RT-PCR and immunoblotting. The inhibition of NO release by neoandrographolide can be attributed to the block of iNOS mRNA transcription followed by inhibiting protein expression. However, neoandrographolide inhibited COX-2 protein expression only but without inhibiting COX-2 mRNA expression, which was involved in the inhibitory activity against the PGE(2 )overproduction. This suggests that the effect of neoandrographolide on iNOS expression may occur at the transcriptional level and the inhibition of COX-2 expression occurs at the translational level. Furthermore, we have found that the addition of neoandrographolide inhibited the activation of p38 mitogen-activated protein kinase (MAPKs) instead of JNK, ERK1/2, or NF-kappaB. These results indicated that the anti-inflammatory properties of neoandrographolide might result from the inhibition of iNOS and COX-2 expression through inhibiting p38 MAPKs activation. Therefore, neoandrographolide isolated from A. paniculata could be offered as a leading compound for anti-inflammation.