Formation of channel-like pores in a plant membrane was induced within seconds after application of an aqueous solution containing regurgitant of the insect larvae Spodoptera littoralis. Gated pore currents recorded on the tonoplast of the Charophyte Chara corallina displayed conductances up to several hundred pS. A voltage-dependent gating reaction supports the assumption that pore-forming molecules have amphipathic properties. Regurgitant samples separated into masses smaller or larger than 3kDa were evaluated by patch-clamp and mass spectroscopy. Fractions containing peptides larger than 3kDa constituted pores of large conductances, peptides smaller than 3kDa constituted pores of small conductances. Peptide-free eluates did not constitute conducting pores, indicating that pore-forming components in regurgitant are membrane-spanning oligopeptides.