Hyperfine splitting patterns of the ESR spectra of 2.2.6.6-tetramethylpiperidine-N-oxyl (TEMPO) in octyl beta-D-glucoside (OG)-containing egg yolk phosphatidylcholine (EPC) large unilamellar vesicle suspensions were mainly composed of TEMPO dissolved in water, in lamellar EPC, and in nonlamellar EPC, Their hyperfine splitting constants and half widths were available for monitoring the behavior of OG in the course of vesicle destruction.