The present invention is directed to a method for treating inflammatory arthritis in a mammal. The method typically comprises administering to an animal a therapeutically effective amount of at least one compound selected from indigo, isoindigo, indirubin or derivatives thereof, such as NATURA-α or NATURA. The present invention is further directed to pharmaceutical compositions that include a therapeutically effective amount of at least one compound of the invention, an anti-inflammatory arthritis agent and a pharmaceutically acceptable carrier.