Flavobacterium psychrophilum, a bacterium known for its adhesion ability to surfaces, has recently been shown to express phenotypic variation, as smooth and rough colony types in vitro. The aim of this study was to assess the effect of differentcompounds on adhesion of both phenotypes of F. psychrophilum to polystyrene surfaces of 96-well microtiter plates. Cells of F. psychrophilum of both phenotypes (108 CFU ml−1) were treated with different compounds for 1 h at 15◦C andweresubsequently allowed to adhere to polystyrene surfaces. The adhered cells were stained with crystal violet and optical density measured at 595 nm. The compounds were classified as non, weak, moderate or strong inhibitors of the F.psychrophilum adhesion. The results showed that a combination of selected carbohydrates, D- and L-amino acids, phytochemicals, an ion chelating agent (EDTA) and proteinase K strongly inhibited the adhesion of mainly smooth cells. Wesuggest that the compounds inhibit the cell adhesion by presumably disrupting the protein–protein interactions that hold smooth cells together and by negatively affecting the surface hydrophobicity of smooth cells. In contrast, rough cells exhibit resistance to most inhibitor compounds.