The adsorption kinetics exhibited by the wild type and two synthetic stability mutants of bacteriophage T4 lysozyme at silanized silica surfaces were monitored with in situ ellipsometry, Mutant lysozymes purified from Escherichia coil strain RRI were produced by substitution of the isoleucine at amino acid position three with cysteine and tryptophan, yielding proteins of greater and lower thermal stability than that of the wild type, Adsorption kinetics were measured over a period of 8 h and interpreted with reference to mechanisms allowing for binding into one of two states, characterized by different binding strengths, Each interpretation suggested that a protein of lower structural stability would more readily undergo a structural change at the interface, all other things being equal, and this change was more pronounced on hydrophilic than on hydrophobic surfaces.