Effect of the various organizational factors that modulate the state of phospholipid in a bilayer as a substrate for phospholipase will be examined. The perturbations in the packing of lipid in bilayer that will be examined are temperature-dependent and additive-induced. The kinetics of phospholipid hydrolysis is to be correlated to the features of bilayer organization including phase separation, rotational and lateral mobility of the substrate. Various assumptions underlying current hypotheses of mechanism of activation of phospholipase action by substrate aggregation and further activation by incorporation of certain additives into aggregates like bilayer will be examined. These results have significant bearing on current concepts of biological heterogeneous catalysis, and on the possible in vivo after-effects and complications induced by lipid soluble compounds including anesthetics, insecticides, organic solvents.