In a small range finding study a number of N-benzylpiperazino derivatives of 3-nitro-4- hydroxycoumarin have been shown to combine potent HI-antihistamine activity with that of mast cell stabilization as demonstrated by their activity as antagonists of histamine on guinea pig ileum and by their inhibition of the release of histamine in rat passive peritoneal anaphylaxis (PPA). The most potent compound, 1-[2-hydroxy-3-[(4-hydroxy-3- ...