The activity of dioxidine under the conditions of aerobiosis was studied with respect to 23 bacterial species (443 strains). High activity of dioxidine against enterobacteria and its less pronounced activity against P. aeruginosa, Staphylococcus and Enterococcus were shown. It was found for the first time that dioxidine was active against H. alvei, M. lacunata, M. nonliquefaciens, A. anitratus, A. lwoffii and P. maltophilia. Comparative activity of dioxidine under the conditions of aerobiosis and anaerobiosis against 21 bacterial species (101 strains) was investigated. It was demonstrated that under the conditions of anaerobiosis the activity of dioxidine increased 4-128 times. The coefficient of the increase in the antimicrobial activity of dioxidine depended on the species and strain of the bacteria and mainly on the initial level of the drug sensitivity. Thus, with respect to the strains having the MIC of 125 to 1000 micrograms/ml or higher under the conditions of aerobiosis the antibacterial activity of dioxidine increased 16-128 times. However, with respect to the highly sensitive strains (MIC of dioxidine under the conditions of aerobiosis was equal to 4-8 mg/ml) the antimicrobial activity of the drug increased only insignificantly i.e. 4-8 times. The results of the study indicated that the use of dioxidine as a reserve drug in treating pyoinflammatory infections such as phlegmon, abscesses, etc., developing at lowered concentrations of oxygen in the tissues was promising.