The analgesic effects of various agents were evaluated in knee joint monoarthritic rats where arthritis was induced by monosodium urate (MSU) crystals injected into the knee joint cavities. The weight supported by each hind limb was measured quantitatively using pressure transducers, which revealed dose-dependent recovery produced by various analgesics including morphine but no changes in value by sedatives such as chlorpromazine. Relative potency obtained from the value of ED50 of each analgesic agent was congruent with that in clinical use. The MSU test may be quite suitable for quantitative and objective evaluation of the analgesic effects of various agents, particularly for spontaneous and tonic pain.