The influence of alkali treatment on wool keratin and on silk fibroin was investigated in a medium of K2CO3 at 50 degrees C. It was found that the denaturing action of LiBr affects the reactivity and reactions of the disulfides differently from stretching of the fibers does. Since the sum total of the sulfur-containing amino acids remains constant during alkali treatment of both native and denatured wool, the participation of cystine in the formation of lysinoalanine is excluded. It is suggested that seryl residues are responsible for the formation of alpha-amino acrylic acid residues which combine with the lysine present in wool or in silk to form lysinoalanine. The sulfur content in wool, as obtained by direct determination, was higher than the expected values, and this indicates the presence of sulfur compounds formed during the alkali treatment, which are not analyzed as any of the known sulfur-containing amino acids. No evidence was found that peptide-bound lanthionine is unstable towards 0.7 M K2CO3 solution at 50 degrees C. A significant increase in N-terminal seryl residues was observed for alkali-treated wool. Various possible explanations of this phenomenon were investigated.