Abstract Background: CancerB (CCB, IMSF-5), herbal combination, may be able to stimulate potential toxic mediators such as nitric oxide (NO) and tumor necrosis factor-alpha (TNF-α) in isolated mouse peritoneal macrophages. Methods: NO production was determined by Griess method, and TNF-α production by enzyme-linked immunosorbent assay. Amounts of proteins were observed by Western blotting. Results: CCB had no effect on NO production by itself, but CCB alone did stimulate the production of TNF-α. When CCB was used in combination with recombinant interferon-γ (rIFN-γ), there was a marked cooperative induction of NO production, TNF-α production and NF-κB activation. The increase in NO synthesis was reflected as an increased amount of inducible NO synthase protein. The increased production of NO from rIFN-γ plus CCB-stimulated peritoneal macrophages was decreased by the treatment with N G-monomethyl- l-arginine or N α-Tosyl-Phe Chloromethyl Ketone. Nuclear factor-kappa B (NF-κB) inhibitor, pyrrolidine dithiocarbamate was able to completely inhibit the production of NO and TNF-α. Conclusions: These findings demonstrate that CCB increases the production of NO and TNF-α by rIFN-γ-primed peritoneal macrophages and suggest that NF-κB plays a critical role in mediating these effects of CCB.