Using the planar lipid bilayer technique, it is shown that a yeast elicitor as well as several cellulolytic enzymes used in protoplasting plant cells contain components which strongly interact with the bilayers. This results in the appearance of transmembrane ion fluxes which may pass through membrane defect structures and even large conductance pores with unitary conductances above 400 pS. Since membrane depolarization is an immediate response in the process of defense elicitation in plant cells, elicitors may act directly with the lipid phase of cell membranes, causing depolarizations and thus initiating the process of elicitation. When using enzymatically prepared protoplasts in electrophysiological work, contributions to electrical activity by membrane active constituents originating from the enzymes used must be expected.