The anti-inflammatory activities of six benzoxazinoids isolated from roots of Coix lachryma-jobi var. ma-yuen and structurally related synthetic materials were investigated by measurement of their inhibition of histamine release from rat mast cells stimulated with concanavalin A (Con A) and sensitized with immunoglobulin E (reagin). Because the inhibition data for either Con A or IgE with these compounds were comparable, Con A can be used for rapid first-stage screening of active compounds. Four glycosides out of the eleven compounds investigated were not active. Other results showed that the free hydroxyl group at the 2-position in the benzoxazinone skeleton is important for the expression of inhibitory activity.