The amino acid composition of isolated cell walls of Bacillus psychrophilus has been determined before and after extraction of protein with ethylenediamine-tetraacetic acid at 45 C. This revealed that the peptidoglycan consists of Ala, Lys, and Glu in a molar ratio of 3:1:2. By using autolytic digests of log-phase cell walls, it was possible to detect 14 ninhydrin-positive degradation products. Chemical analyses of the seven major bands from these digests indicated that the amino acid sequence of the peptide subunit in the murein of this organism consists of muramyl-l-alanyl-gamma-d-glutamyl-l-lysyl- d-alanine, and the linkage between adjacent peptides is supplied by a second d-glutamic acid which is bound to the sigma-amino group of lysine and the carboxyl group of the d-alanine through its amino group. The nature of the solubilized wall fragments indicates that each of the peptide bonds in the murein is hydrolyzed by autolysins except the l-alanyl-gamma-d-glutamyl linkage.