Abstract: The invention is directed to pharmaceutical and veterinary preparations having antibacterial action characterized by the contents of the following two bactericidally active substances(1) a rifamycin compound(2) a nitrofuran compoundThey show a synergistic enhancement of the bactericidal action as compared with the single antibactericidal components when given alone and they also suppress or prevent the development of resistance towards these antibiotics or antibacterial agents, especially towards rifampicin. Preferred ratios of the quantities of (1) and (2) contained in these preparations are 6:1 and 2:1. An especially suitable combination is rifampicin and nitrofurantoin. Other examples are the combination of 3-amino-rifamycin SV derivaties with known nitrofuran derivatives, such as nitrofurantoin, furzolidone or furaltadone.