Dioxidine sensitivity of 267 clinical strains of aerobic bacteria was determined with the method of two-fold serial dilutions in agar. The strains were cultivated under aerobic and anaerobic conditions. The sensitivity of 96 anaerobic bacteria was also estimated. When the aerobic bacteria such as Enterobacteriaceae, Staphylococcus spp., Streptococcus spp. and P. aeruginosa were grown under anaerobic conditions i.e. under conditions more close to the real ones in the infection foci their sensitivity increased. There was observed a relationship between dioxidine sensitivity of the bacteria under aerobic and anaerobic conditions which was expressed by the following equation: y = 4.73 + 0.666x. Under anaerobic conditions the Enterobacteriaceae strains were more sensitive to dioxidine (MIC90 2-3 micrograms/ml) than gram-positive aerobic cocci (MIC90 64-256 micrograms/ml). At a concentration of 2 micrograms/ml dioxidine inhibited the growth of the majority of anaerobic species: Bacteroides, Fusobacterium, Clostridium and anaerobic cocci.