The plasma membrane H(+)-ATPase which plays a central role in plant cell physiology is lipid-dependent enzyme. Lipid composition of plasma membrane can be modified by the action of endogenous phospholipases. Recently it has been supposed that the plasma membrane phospholipase A2 participates in phytohormonal signal transduction on the H(+)-ATPase protein. We have investigated the effect of phospholipase A2 on the H+ ATPase activity in plasma membrane preparations isolated from 7-days corn seedling roots. The exogenous phospholipase A2 from snake venom and lipid hydrolysis products of the phospholipase A2-catalysed reaction have been used. It was found that the phospholipase A2 increased plasma membrane H(+)-ATPase activity during first 15 sec. but inhibited it under the longer exposition. Examination of lyso-derivatives effect on plasma membrane preparations demonstrated a 2-3-fold increasing of their H(+)-ATPase activity by lysophosphatidylcholine whereas the effect of lysophosphatidic acid was expressed to higher extent. Studying of the effects of unsaturated free fatty acids as the second hydrolysis product has shown that linolic and linolenic acids activated the plasma membrane H(+)-ATPase at concentration of 10 microM but inhibited it at higher concentrations. Exposition of plasma membranes with the phospholipase A2 or fatty acids shifted H(+)-ATPase pH optimum from pH 6.5 to pH 7.0. The role of endogenous phospholipase A2 in regulation of plasma membrane H(+)-ATPase activity has been under discussion.