Nifurzide, a synthetic antimicrobial agent of the nitrofuran group. The MICs were excellent for Campylobacter spp. (97 strains); slightly higher for Shigella spp. (50 strains) and Aeromonas spp. (22 strains); and highest for Salmonella spp. (100 strains) and Yersinia enterocolitica. At low concentrations of nifurzide, the growth rate of the Escherichia coli cultures decreased, and elongated, nonseptate cells appeared. At high concentrations, complete growth inhibition occurred, accompanied by a rather strong bactericidal effect, but the appearance of the cells was normal; in particular, no bacteriolytic effect was observed. A very large number of antibiotic molecules were bound per bacterial cell. After cell disruption, similar amounts of nifurzide were found in the cytoplasm, cytoplasmic membranes, and cell wall, respectively. Nifurzide had no effect on a general infection, but significantly decreased the number of colony-forming germs in the digestive tract. It was rather insoluble in aqueous media, did not cross the intestinal barrier, and was not substantially metabolized in the intestine. The obnoxious side effects of other nitrofurans (induction of vomiting and inhibition of monoamine oxidase) were not observed with nifurzide, which makes it an interesting therapeutic agent against enteric infections.