A new group of chemical agents with pronounced antibacterial activities is presented. Different nitrothiazole derivatives, but not all, exhibit antibacterial activities similar to that of niridazole (AmbilharR), a nitrothiazolyl-imidazolidinone. Certain aerobic bacteria are moderately susceptible to these agents. The efficacy of these agents is almost comparable to that of ampicillin and tetracyline. It is much better than the efficacy of nitrofuran derivatives, the nitroimidazole derivatives being inactive. The mode of action of the nitrothiazole derivatives is bactericidal. Against anaerobic bacteria the nitrothiazole derivatives are unique, since the extremely low MIC's are not approached by any other of the nitro-compounds nor by any other of the common antibiotics tested, such as clindamycin, ampicillin and tetracycline. It is suggested that the nitrogroup of the nitrothiazole ring moiety represents the chemical structure responsible for their excellent antibacterial activities.