The development of transgenic techniques has accentuated the need for valid disease models in mice. In the present study, we have in female mice characterized adjuvant-induced monoarthritis, an inflammatory model which is commonly used in rats. Freund's complete adjuvant (FCA), 20 microl, was injected into the left knee joint. Pain was inferred from impairment of gait and stance. Two commonly used mouse strains were compared. Outbred NMRI mice showed significant levels of pain behaviour lasting for at least 7 days after injection of FCA while inbred BALB/c mice showed altered behaviour at 3, but not at 5 days. The effects of three commercially available preparations of FCA were compared in NMRI mice. All adjuvants caused highly reproducible spontaneous pain behaviour at 1-3 days with a reduction at 5 days and no significant pain-related behaviour at 10 days. Intraarticular injection of 2% carrageenan performed for comparison, caused pain-related behaviour for less than 24 h. The adjuvant-induced pain behaviour was dose-dependently reduced by 3-30 micromol/kg morphine and 3-30 micromol/kg diclofenac. In conclusion, adjuvant-induced monoarthritis in mice provides a robust model for pharmacological studies of inflammatory pain, but the choice of mouse strain is important for the outcome.