The synthesis of a series of [1,4]benzoxazine-2,3-diones and a new class of compounds, benzobisoxazinetetrones, is described. These compounds were evaluated for their effect in the rat mast cell (RMC) test passively sensitized in vitro with rat antiovalbumin serum and for their effect in inhibitory passive cutaneous anaphylaxis (PCA) in the rat. Some of these compounds are of the same potency level as disodium cromglycate in the RMC test and some are effective orally in PCA.