Eight cases of contact allergy to virginiamycin are reported. In all patients patch tests with fractions of both virginiamycin (factor M and S) and pristinamycin (fraction IA and IIA) were performed. All patients allergic to virginiamycin, reacted also to pristinamycin, factor M and fraction IIA. Chemically, factor M and fraction IIA appeared to be completely identical, implicating that we are dealing with false cross-sensitivity.