In this study, the anti-inflammatory effects of a tropolone derivative, 2,5-dihydroxycyclohepta-2,4,6-trienone (AD-4), were investigated. The anti-inflammatory potency of AD-4 was compared with that of indomethacin in carrageenan-induced inflammation models in rats. The effect on vascular permeability was also determined by hyaluronidase-induced capillary permeability. AD-4 decreased carrageenan-induced paw edema at doses of 3.62 x 10(2), 7.24 x 10(2), and 14.48 x 10(2) mu mol/kg by 45% (p < 0.001), 79% (p < 0.001), and 83% (p < 0.001), respectively, compared with the value of 49% (p < 0.001) for indomethacin (69.8 mu mol/kg). Additionally, AD-4 decreased hyaluronidase-induced capillary permeability significantly. In conclusion, AD-4 was determined to have anti-inflammatory effects with lower toxicity than indomethacin. Anti-inflammatory effect of AD-4 may be related to its effects on vascular permeability.