C-13 n.m.r. spectra of low sulfur fraction in S-(carboxymethyl) keratine, (SCMKA), which corresponds to the hard keratin intermediate filament (KIF) in human hair were observed in aqueous solution. The spectra were compared with those of SCMKA in 8 M urea and high sulfur fraction in S-(carboxymetyl) keratine, (SCMKB), in aqueous solution. The circular dichroism spectrum of SCMKA indicated 40% alpha-helix in the aqueous solution, and changed to that of random coil in 8 M urea. The SCMKB in aqueous solution also took random coil. The observed peaks in the C-13 n.m.r. spectra of SCMKA in aqueous solution come mainly from the amino acid residues such as Thr, Ser, Pro and Gly in the N- and C-terminal domains with random coil structure. Thus it is suggested that these domains had high mobility. However, the amino acid residues, Leu, lie, Gin, Arg and Lys, in the rod domain give essentially no peaks because of very restricted motion of the chain with coiled-coil structure.