The antimycotic potency of 2,4-dihydroxythiobenzanilide derivatives was tested. The MIC assessments by an agar dilution method were used for the estimation of potential activity in vitro against the four mould strains: Scopulariopsis brevicalis, Aspergillus niger, Aspergillus fumigatus and Penicillium sp. The strongest fungistatic activity was observed for 3'-fluoro-derivative (MIC 7.82 microg/ml). It was stated that the inhibition action of these compounds depends mainly on lipophilicity of molecules. Parabolic relationships between the antimycotic activity and lipophilicity were found.