The interaction of three high hydrophilic-lipophilic balance (HLB), water soluble sucrose monoesters with β-lactoglobulin and β-casein from bovine milk was studied by fluorescence titration and equilibrium dialysis techniques. The β-lactoglobulin bound all forms of the sucrose ester investigated stoichiometrically with a single, comparatively high affinity site. In contrast, β-casein bound the emulsifier substoichiometrically, possibly by interaction with β-casein micelles. The interaction of lauryl and stearoyl sucrose esters with β-lactoglobulin was stronger than with β-casein. The affinity of binding increased with saturated fatty acid chain length for both proteins, with the stearoyl ester giving a dissociation constant of 2.3 μ.M with β-lactoglobulin. However, the interaction of the monounsaturated oleic sucrose ester with β-casein was marginally stronger than with β-lactoglobulin.