From the culture broth of Bacillus cereus 60-6, in which antibiotic production was improved a new antibiotic, named cerexin C, was isolated. Similarly, a new antibiotic, cerexin D was isolated from the culture broth of Bacillus cereus Gp-3. Cerexins C and D are closely related to cerexins A and B in their physico-chemical and antimicrobial properties. In fact cerexins C and D are peptides essentially identical with cerexins A and B except for the presence of a lysine residue in place of the gamma-hydroxylysine residue.