Methylsulfonylmethane (MSM), also known as dimethyl sulfone and methyl sulfone, is an organic sulfur-containing compound that occurs naturally in a variety of fruits, vegetables, grains, and animals, including humans. In the present study, we demonstrated the anti-inflammatory effects of MSM in lipopolysaccharide (LPS)-stimulated murine macrophages, RAW264.7 cells. MSM significantly inhibited the release of nitric oxide and prostaglandin E(2) by alleviating the expression of inducible nitric oxide synthase and cyclooxygenase-2 in LPS-stimulated RAW264.7 cells. Furthermore, the levels of interleukin-6 and tumor necrosis factor-alpha were decreased by MSM treatment in cell culture supernatants. Further study indicated that the translocation of the p65 subunit of nuclear factor (NF)-kappaB to the nucleus was inhibited by MSM treatment in LPS-stimulated RAW264.7 cells, in which it helped block degradation of inhibitor of NF-kappaB. In addition, in vivo studies demonstrated that topical administration of MSM at 500-1250 microg/ear resulted in similar inhibitory activities in 12-O-tetradecanoylphorbol 13-acetate-induced mouse ear edema. Collectively, theses results indicate that MSM inhibits LPS-induced release of pro-inflammatory mediators in murine macrophages through downregulation of NF-kappaB signaling.