The effect of cationic polymers and surface active substances (SAS) on sensitivity of Klebsiella aerogenes 600, Escherichia coli 154 and Proteus vulgaris 7470 to kanamycin was studied. A decrease in the resistance of the above organisms to kanamycin on its use in combination with cationic polymers and SAS was observed. It was shown that such substances inhibited the activity of the enzymes inactivating kanamycin. Their effect was suggested to be due to changes in the lipid surrounding of the enzymes.