1. A study has been made of peptide excretion in twenty cases of Wilson's disease, ligand-exchange column chromatography being used to separate peptides from free amino acids. Previous reports of excess of peptide output in the disease were confirmed and the excess was shown to be highly significant statistically.
2. A considerable fraction of the excess of peptide output was shown to consist of hydroxyproline-containing peptides derived from collagen degradation.
3. The method of rank correlation showed that the difference both in free amino acid and peptide-bound amino acid output in cases of Wilson's disease and in control subjects was mainly quantitative; the pattern of amino acid excretion was qualitatively similar in both groups.
4. Evidence is presented that the increased copper output in the urine in the disease is not secondary to peptiduria.