The increased membrane permeability for K+, glycerol and erythritol, and membrane lysis induced by alkyl and alkenyl resorcinols, respectively, might be due to the interaction with membrane proteins and the formation of reversed micelles. The 5-(n-alk(en)yl) resorcinols show a very high stability at the air/water interface. The molecular area is 0.28 and 0.37 nm2 (at 30 mN/m) for alkyl and alkenyl resorcinols from rye, respectively. Differential scanning calorimetry experiments show a miscibility of alk(en)yl resorcinols with phosphatidylcholines. Only for alkenyl resorcinols is a small reduction found in the free energy of dipalmitoyl phosphatidylcholine. Electron microscopy studies show protein patching in erythrocyte membranes after the addition of resorcinols. The resorcinol-induced K+ release is not influenced by the presence of proteolytic enzymes, but strongly reduced by bovine serum albumin and glycophorin. 31P-NMR measurements show the occurrence of an isotropic and hexagonal signal in egg phosphatidylcholine in the presence of about 30 mol% alk(en)yl resorcinol.