The effect of tea polyphenols on the release of chemical mediators, histamine and leukotriene B4 (LTB4), from rat peritoneal exudate cells (PEC) was studied. Among polyphenols, (-)-epigallocatechin gallate (EGCG) most strongly inhibited the histamine release from the cells stimulated with a calcium ionophore, A23187 or compound 48/80. Though (+)-catechin (C) and (-)-epicatechin (EC) had no effect, (-)-epigallocatechin (EGC) and (-)-epicatechin gallate (ECG) moderately inhibited the histamine release. Similarly, EGCG, ECG, and EGC inhibited LTB4 release from PEC, whereas C and EC were not effective. The magnitude of the inhibitory effect on the release of these mediators of tea polyphenols was in the order of EGCG > ECG > EGC. These results indicated an important role of the triphenol structure in the inhibitory activity. Therefore, the possible antiallergic effect of tea polyphenols can be expected.