High amounts of nitric oxide (NO) production following the induction of inducible NO synthase (iNOS) gene expression has been implicated in the pathogenesis of inflammatory diseases. Capsaicin, a vanilloid receptor agonist, is known to have an inhibitory effect on NO production in macrophages. In the present study, we have found that capsazepine (CAPZ), a vanilloid receptor antagonist, also inhibited NO and iNOS protein syntheses induced by lipopolysaccharide in RAW264.7 macrophages via the suppression of iNOS mRNA. The mechanistic studies showed that CAPZ inhibited the expression of iNOS mRNA through the inactivation of nuclear transcription factor-kappa B (NF-kappa B). Thus, capsazepine may be a useful candidate for the development of a drug to treat inflammatory diseases related to iNOS gene overexpression.