Treatment of leukemic HL-60, NIH 3T3, and baby hamster kidney (BHK-21) cells, prelabeled with [2-14C]ethanolamine, with 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent activator of protein kinase C, resulted in increased degradation of both 14C-labeled phosphatidylethanolamine and its alkenyl (plasmalogen) derivate. A half-maximal and a maximal (approximately 3.4-fold) stimulation of ethanolamine phospholipid degradation required 3 and 10-20 nM TPA, respectively. TPA had a similar concentration-dependent stimulatory effect on the hydrolysis of phosphatidylcholine in cells previously prelabeled with [methyl-14C]choline. Increased phospholipid degradation was not accompanied by the formation of lysophosphatidylethanolamine, indicating that a phospholipase A-type enzyme was not involved. About 80% of total water-soluble degradation products was ethanolamine, suggesting that phospholipid hydrolysis was catalyzed by a phospholipase D-type enzyme. Increased formation of ethanolamine with exposure of cells to TPA was observed only after a 10-min lag period. Mezerein, bryostatin, sn-1-oleoyl-2-acetylglycerol, and polymyxin B, all of which mimic the action of TPA on protein phosphorylation in vivo, also stimulated the hydrolysis of ethanolamine phospholipids in HL-60 cells, suggesting that the TPA effect was mediated by protein kinase C.