On oxidizing wool by performic acid a soluble protein fraction is obtained containing high amounts of tyrosine, phenylalanine and glycine. This fraction, termed “δ‐keratose”, is extremely heterogeneous as shown by solubility characteristics, electrophoresis and end‐group determination. Anion‐exchange chromatography allows isolation of subfractions with different amino‐acid compositions. This process, however, involves a marked loss of tyrosine‐rich proteins absorbed irreversibly. Repeated preparative electrophoresis on polyvinylchloride layers permits isolation of many subfractions on a preparative scale without loss of aromatic amino acids. The amino‐acid composition of these subfractions is investigated. In spite of the wide differences among them some common features for all fractions can be established. It is shown that possible contamination by other proteins is not responsible for the heterogeneity of δ‐keratose but rather due to a wide variation in the amino‐acid composition among the demonstrated tyrosine‐rich proteins.