This invention provides a new therapeutic or prophylactic agent for arthritissuch asosteoarthritis. Specifically, it provides a therapeutic or prophylactic agentfor arthritis suchas osteoarthritis, or an agent for promoting the growth of articularchondrocyte, comprising aguanyl cyclase B (GC-B) activator as an active ingredient； or a method forinhibiting arthritisor for promoting the growth of articular chondrocyte by activating GC-B； or amethod forscreening an agent for promoting the growth of articular chondrocyte or anagent capable oftreating arthritis using the GC-B activity as an indication.
