The term lipase is used to describe any enzyme activity causing the hydrolysis of lipids and long-chain acyl esters. A lipid biochemist is well aware of the high activities of lipolytic enzymes in many plants. The extraction and analysis of lipids, or of lipid-dependent membrane and enzyme preparations, are frequently severely affected by the presence of endogenous lipolytic activity. Methods for lipid extractions with plant materials have been developed to take account of potential degradation—normally by inactivating the relevant enzymes before extracting the lipids. Unwitting use of methods developed in mammalian biochemistry gives rise to artifacts and errors, and the problem is confounded by the fact that some lipolytic enzymes are activated by the organic solvents used in lipid extractions. Lipolytic enzymes are considered hydrolases using water as a co-substrate. However, most hydrolases act also as transferases when the cosubstrate is ROH.