Adsorption of the amino acid tryptophan, the peptide tryptophan-leucine and the protein bovine serum albumin (BSA) at buffered water-oleyl alcohol interfaces has been studied by ellipsometry. Tryptophan-leucine solutions showed a systematic change in ellipticity with concentration indicating an adsorption of 0.5 mg/m(2) for a solution concentration of 1 g/L and evidence of saturation at that concentration, ESA showed an adsorption of 0.45 mg/m(2) for a concentration of 3.5 g/L with no sign of saturation, There appeared to be little adsorption of tryptophan at the interface.