Many studies have been carried out in recent years on the pharmacological effects of nigella sativa seeds that have uncovered their anflinflammatory and immunological effects. The objective of this study was to explore the anflinflammatory effects of thymoquinone on arthritis in rat models. Rats with arthritis induced by Freund's incomplete adjuvant were assigned into five groups: group 1: controls 0.9% NaCl (n = 7); group 2: 2.5 mg/kg thymoquinone (n = 7); group 3: 5 mg/kg thymoquinone (n = 7); group 4: Bacilli Chalmette Guerin (BCG) 6 x 10(5) CFU (n = 7); group 5: methotrexate 0.3 mg/kg (n = 7). Signs of inflammation on the claw and radiological signs were searched for and TNF-alpha and IL-1beta were measured. The results of control and other groups were compared. As a result, thymoquinone, confirmed clinically and radiologically, suppressed adjuvant-induced arthritis in rats. Copyright (c) 2006 John Wiley & Sons, Ltd.