Dipyrone, a pirazolone derivative, is a known analgesic drug with minor toxic effects associated with its administration. The aim of the present study was to determine the analgesic and antiinflammatory effects of dipyrone in a model of chronic inflammation (adjuvant-induced arthritis in rats). Hind-paw hyperalgesia was detected in arthritic rats from the 10th to the 16th day of observation. Edema development was maximum (twofold increase) at the 14th day of observation compared to control animals and reduced at the 16th day of observation. Dipyrone (1-50 mg/kg) dose-dependently reduced both hind-paw hyperalgesia and edema from arthritic rats. However, it was shown to be more potent as analgesic than antiinflammatory in the present model. In contrast, indomethacin (2 mg/kg) and dexamethasone (0.4 mg/kg) completely inhibited hind-paw hyperalgesia and edema development. Our results indicate that dipyrone reduced the hyperalgesia and edema in arthritic rats by a mechanism not involving release of prostaglandin-like substances. The possibility of dipyrone inducing analgesia in arthritic rats through a peripheral action supports the use of dipyrone as an alternative choice drug for the treatment of pain associated with arthritislike diseases in selected cases.