We show that epigallocatechin-3 gallate (EGCG), a major component of green tea, stimulates phospholipase D (PLD) activity in U87 human astroglioma cells. EGCG-induced PLD activation was abolished by the phospholipase C (PLC) inhibitor and a lipase inactive PLC-gamma1 mutant, which is dependent on intracellular or extracellular Ca(2+), with the possible involvement of Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II). EGCG induced translocation of PLC-gamma1 from the cytosol to the membrane and PLC-gamma1 interaction with PLD1. EGCG regulates the activity of PLD by modulating the redox state of the cells, and antioxidants reverse this effect. Moreover, EGCG-induced PLD activation was reduced by PKC inhibitors or down-regulation of PKC. Taken together, these results show that, in human astroglioma cells, EGCG regulates PLD activity via a signaling pathway involving changes in the redox state that stimulates a PLC-gamma1 [Ins(1,4,5)P(3)-Ca(2+)]-CaM kinase II-PLD pathway and a PLC-gamma1 (diacylglycerol)-PKC-PLD pathway.