In this study, 1-naphthol has been used as a sensitive ESPT fluorescent molecular probe to investigate the interaction of submicellar concentrations of two physiologically important bile salts, sodium deoxycholate and sodium cholate, with dipalmitoylphosphatidylcholine small unilamellar vesicles in solid gel and liquid crystalline phases. Steady-state and time-resolved fluorescence of the two excited state prototropic forms of 1-naphthol indicate that the incorporation of monomeric bile salt molecules in the lipid bilayer membrane induces appreciable wetting of the bilayer up to the hydrocarbon core region, even at very low (<= 1 mM) concentrations of the bile salts.