It has been reported that the pharmacological characteristics of bisphosphonates vary depending on the side chain attached to the carbon atom of the P-C-P bond. TRK-530 is a novel synthetic bisphosphonate with an anti-oxidant methylthio-phenylthio side chain. This compound has been suggested to have both anti-inflammatory and anti-bone-resorbing effects. Such a compound could be effective for the treatment of diseases with excessive bone resorption accompanied by inflammation. We have been studying this compound as a potential therapeutic agent for periodontitis. To date, we have found that 1) TRK-530 inhibited osteoclastic bone resorption in animals and in bone organ culture, 2) both systemic and topical administration of TRK-530 prevented alveolar bone loss in animals with experimental periodontitis, 3) TRK-530 prevented prostaglandin E(2) synthesis by inhibiting the expression of cyclooxygenase (COX)-2 mRNA, and 4) TRK-530 inhibited the formation of dental calculus. The above results suggest that TRK-530 might be useful for the treatment of alveolar bone loss in periodontitis.