Deuterium NMR spectroscopy was applied to a study of conformational dynamics of alkyl chains in the lamellar phase of a C12E3 (nonionic surfactant)-water system. The order parameter derived has shown that addition of the surfactant in the lamellar phase causes conformational disordering of alkyl chains, leading to a transition to an isotropic solution phase, while addition of water, which eventually leads to phase separation, causes no substantial disordering of alkyl chains.