The repeated use of an enrichment technique for establishment of antibiotic production in liquid culture, where previously production had only been seen on agar, resulted in the selection of stable strain variants with enhanced resistance to fragmentation. The variant was more resistant to tunicamycin, an inhibitor of peptidoglycan biosynthesis, than the wild-type. When peptidoglycan synthesis was compared in the variant and the wild-type strains of one of the isolates, enhanced activity of the enzyme : phospho-N-acetylmuramyl pentapeptide translocase (which catalyses the first membrane bound reaction of cell wall synthesis) was found in the fragmentation-resistant form.