The leaves of Acanthus ebracteatus, stembark of Oroxylum indicum and the stems of Cryptolepis buchanani and Derris scandens are used as traditional remedies in Thailand for arthritis. Aqueous and alcoholic extracts were tested using three different in vitro systems for effects relevant to anti-inflammatory activity. The aqueous extracts of O. indicum and D. scandens significantly reduced myeloperoxide release. Eicosanoid production was reduced only by the aqueous extracts of A. ebracteatus and D. scandens. D. scandens extract showed potent inhibitory activity against generation of leukotriene B4 and also displayed antioxidant activity. In the rat hind paw edema test, D. scandens extract showed significant activity when given intraperitoneally but did not produce a significant reduction when given orally. The results therefore supported to some extent the traditional use of D. scandens for arthritic conditions and provided slight indication of activity which could explain the use of O. indicum and A. ebracteatus. No relevant activity was demonstrated in any of the tests for C. buchanani extracts.