['Hydrogen sulfide (H(2)S), the main component of halitosis, is one of the etiologic factors for periodontitis. We recently reported that H(2)S may induce pathologic changes in rat alveolar bone. The objective of this study is to determine the effect of H(2)S on osteoclast differentiation.', 'Murine macrophage cells RAW264 were cultured in medium lacking nuclear factor κB ligand (receptor activator of nuclear factor κB ligand) in 5% CO(2) with air at 37°C for 24 hours; then 0.05, 0.5, or 5 ng/ml H(2)S was added to the CO(2)-air mix for 4 days. The controls received the CO(2)-air mix with no H(2)S. Cell differentiation was evaluated by counting the tartrate-resistant acid-phosphatase (TRAP)-positive cells. Extracellular signaling-regulated kinase1/2 (ERK1/2) and mitogen-activated protein kinase p38 phosphorylation were examined by Western blotting. The bone-resorption activity was determined with the resorption assay of calcium phosphate.', 'There were significantly more TRAP-positive cells at a concentration of 0.05 ng/ml H(2)S than at the other concentrations (P <0.001). Cathepsin K protein, a specific marker for osteoclasts, was expressed in the H(2)S-induced multinuclear cells. Resorption of calcium phosphate significantly increased in the H(2)S-induced TRAP-positive cells cultured on plates coated with calcium phosphate apatite (P <0.01). The phosphorylation of ERK1/2 and p38 were accelerated by H(2)S, and increased with time. PD98059 and SB203580, specific inhibitors of ERK1/2 and p38, suppressed the activation of these enzymes and osteoclast differentiation by H(2)S.'] Does oral malodorous compound induce osteoclast differentiation without receptor activator of nuclear factor κB ligand?