Small-angle neutron scattering on large extruded unilamellar dimyristoyl phosphatidylcholine (DMPC) liposomes was used to determine the DMPC bilayer thickness dL and its change in the presence of N-lauryl-N,N-dimethylamine N-oxide (LDAO). At 36 degrees C, the values of dL are dL = 3.44 +/- 0.10 nm and dL = 2.90 +/- 0.10 nm in pure DMPC bilayers and in bilayers at DMPC:LDAO = 2:1 molar ratio, respectively. Using the specific volumes of DMPC and LDAO and supposing that the molecular volumes and surface areas in the bilayer are additive, the surface areas of DMPC (ADMPC) and of LDAO (ALDAO) were found to be at 36 degrees C: ADMPC = 0.644 +/- 0.018 nm2 and ALDAO = 0.25 +/- 0.05 nm2.