Transthyretins isolated from different species bind hydrophobic compounds and are often obtained in a yellow form. Such a transthyretin from chicken serum was purified by chromatography using Sepharose-coupled human retinol-binding protein. The yellow chromophore was extracted with methanol and purified by reverse phase HPLC followed by normal-phase chromatography on a nitrile column. Ultraviolet-visible absorbance and mass spectrometry identified the yellow compound as lutein, i.e. xanthophyll, (all-trans)-beta, epsilon-carotene-3,3'-diol, estimated to constitute 10-30% of associated colourless compounds. These components are different from the yellow component isolated from human transthyretin and establish that carotenoid-derived pigments can be associated with transthyretins.