The effect of Withania somnifera Linn. Dunal (Solanaceae) on adjuvant arthritic rats was studied and compared with that of indomethacin. The anti- inflammatory activity of Withania somnifera was assessed by measuring paw swelling and lysosomal enzyme activity in control and experimental rats. Increased paw diameter and lysosomal enzyme activity in the arthritic animals were significantly suppressed to near normal levels in rats treated with 1000 mg kg-1 Withania somnifera root powder and 3 mg kg-1 indomethacin. These results indicate that Withania somnifera has promising anti-arthritic activity as a result of its stabilizing action on lysosomal enzyme activity.