1. S-Carboxymethylkerateines extracted from normal hair can be fractionated into high-sulphur and low-sulphur proteins similar to those obtained from sheep's wool. Normal human hair gives a major high-sulphur protein of higher molecular weight and S-carboxymethylcysteine content than any isolated from normal sheep's wool. 2. The proteins from cystine-deficient hair can also be divided into high-sulphur and low-sulphur proteins. There is a lower proportion of high-sulphur protein in cystine-deficient hair than in normal hair. 3. The high-sulphur proteins from cystine-deficient hair have an abnormal amino acid composition and in particular are lower in S-carboxymethylcysteine content than the corresponding proteins from normal hair. New components are present and the content of very high-sulphur proteins of high molecular weight is much decreased. The low-sulphur proteins of cystine-deficient hair are probably also deficient in S-carboxymethylcysteine. 4. The proteins of cystine-deficient hair probably resemble those in the normal hair root, except that disulphide-bridge formation has occurred.