A knowledge of the physico-chemical surface properties of a bacterium is important to predict the first step in the adhesion process of such a microorganism to biomaterials. In this work, hydrophobicity, surface free energy and surface charge of Enterococcus faecalis ATCC29212 and E. feecalis 72 bacterial strains have been analysed under the followings conditions, which were considered as criteria that could affect the thermodynamical parameters of the cell surface: culture medium was supplemented with serum and urine and the experiments were carried out in two different buffers (KPi and PBS) and at two temperatures (22 and 37degreesC). MATH hydrophobicity does not seem to be affected by temperature but water contact angle increased with temperature for both strains. Serum and urine added to the culture medium made the strains more and less hydrophobic, respectively. The zeta potential was dependent on the addition to the culture medium of serum and urine, the experimental temperature and the buffer employed and it decreased with increasing ionic strength in all cases studied. The results reveal that physico-chemical surface properties of bacteria are greatly affected by the environmental conditions in which they are measured, indicating that experiments should be carried out under experimental conditions as similar as possible to the situation of clinical interest.