The adhesion of Staphylococcus aureus ATCC 25923 to glass at different pH values was investigated using scanning electron microscopy (SEM) and image analysis with the Mathlab((R)) program. The images obtained by SEM show that the adhesion behaviour of Staphylococcus aureus ATCC 25923 depends on the pH of the suspending medium. At highly acidic (pH 2, pH 3) and alkaline pH, the cells deposited in aggregate forms, while at pH 5 the aggregation phenomenon was absent. The quantitative adhesion (number of adhering cells to glass surface) showed that cells adhered strongly in the pH range 4 to 6 and weakly at highly acidic (pH 2, pH 3) and alkaline pH. Moreover, the surface properties of the cells were characterized by the microbial adhesion to solvents (MATS) method. A good correlation was obtained between physicochemical properties (hydrophobicity or electron donor electron acceptor character) of Staphylococcus aureus ATCC 25923 and the number of adhering cells to glass. These results show that the adhesion of Staphylococcus aureus ATCC 25923 to glass is controlled by both acid-base and hydrophobic interactions.