The effect of quaternary ammonium salts (QAS) and amine oxides (AO) on the surface hydrophobicity of a clinical isolate of Enterobacter cloacae was studied. The surface hydrophobicity was evaluated by the method of bacterial adherence to hydrocarbon - xylene and on the basis of salt aggregation test of ammonium sulfate. The efficacy of amphiphilic compounds tested depended on the length of the carbon chain in their molecule. A strong inhibition of adherence of the studied strain to xylene was caused by ATDBr (QAS with the carbon chain) in the whole concentration range. At highest concentration tested, 50 µg cm-1, it decreased the adherence to 18.1 % against the control. The amine oxide TMABr with the side carbon chain inhibited the adherence, but not so strong as ATDBr. Both types of amphiphilic compounds without carbon chain (TMABr and TMANO) were ineffective in the influencing of the surface hydrophobicity of tested strain, or caused moderate stimulation (TMABr, P < 0.05) or inhibition (TMANO) of adherence, respectively, which was statistically insignificant.