A search for possible degradation products of murein, originating from the action of penicillin on growing cells of E. coli B has been made. 2.6-Diaminopimelic acid-containing oligopeptides were isolated from penicillin-induced spheroplasts; the chemical structure of one of these components is identical with that of the peptide side chain of the muropeptides of normal cells. Other peptides, possibly enzymatic breakdown products of the latter, were also identified. The spheroplasts further contained uridine diphosphate muramylpeptides, regarded as precursors of the murein.