Acid hydrolysis revealed that the antibiotic cerexin A is constructed with aspartic acid (3), threonine (1), serine (1), valine (2), allo-isoleucine (1), gamma-hydroxylysine (1), tryptophan (1), and a variety of fatty acid residues. The essential difference between cerexins A and B is concluded to be replacement of serine and one valine residue in cerexin A by glycine and phenylalanine in cerexin B. Isolation of a new amino acid L-threo-gamma-hydroxylysine is also described.