Nicotinamide, a pellagra-preventive factor, has multiple functions such as inhibition of poly-ADP-ribose synthetase, inhibition of inducible nitric oxide synthase, free radical scavenging and suppression of major histocompatibility complex class II expression and ICAM-1 expression on endothelial cells. In addition to these, we have found an inhibitory effect of nicotinamide on production of tumor necrosis factor-alpha (TNF-alpha) in vitro and in vivo. Lipopolysaccharide (LPS)-induced in vitro TNF-alpha production by human peripheral blood mononuclear cells, measured by enzyme-linked immunosorbent assay (ELISA), was significantly inhibited with more than 1 x 10(-3) mol/l of nicotinamide, while interleukin-1-beta was not inhibited and interleukin-6 was slightly inhibited even with 10(-2) mol/l. Oral administration of nicotinamide with more than 62.5 mg/kg also significantly inhibited LPS-induced serum TNF-alpha production measured by ELISA and bioassay in Balb/c mice. Thus, nicotinamide has an inhibitory effect on TNF-alpha production that may be beneficial to TNF-alpha-mediated diseases.