The effect of boswellic acids on bovine serum albumin (BSA)-induced arthritis in rabbits was studied. Oral administration of boswellic acids (25, 50 and 100 mg/kg/day) significantly reduced the population of leucocytes in a BSA-injected knee and changed the electrophoretic pattern of the synovial fluid proteins. The local injection of boswellic acids (5, 10 and 20 mg) into the knee 15 min prior to BSA challenge also significantly reduced the infiltration of leucocytes into the knee joint, reduced the infiltration of leucocytes into the pleural cavity and inhibited the migration of PMN in vitro. The leucocyte-inhibitory activity of boswellic acids was not due to its cytotoxic effect. The boswellic acids did not show any detergent or surfactant properties.