Bacterial quorum-sensing represents an ubiquitary regulating system in which the pheromones (small molecules with different chemical structures, i.e. homoserin-lactones, octapeptides, aminoacids) act as extracellular mediators of signaling and intercellular communication. This chemical system is implicated in the regulation of different physiological processes dependent on the cell density (i.e. biolumniscence, virulence factors expression, sporulation, conjugation, antibiotic secretion etc). It is also mentioned in the literature the implication of bacterial pheromones in the modulation of eukariotic cells division rate. The objectives of this study were: a) to determine the exo-enzymatic profile of bacterial cultures in different growth phase in order to establish potential relationships between the phenotypic expression of some virulence factors on one side and the growth phase and bacterial culture density, on the other side; b) to determine de cytotoxic effect and the influence of bacterial culture supernatants on the HEp-2 cell division rate. Supernatants of bacterial cultures in nutrient broth of 2, 5 and 24 hrs of Staphylococcus aureus and Proteus sp. were tested directly and also, after thermic inactivation (at 100 degrees C, for 5 minutes) for the presence of different enzymatic activities known as virulence factors (spot and Kanagawa haemolysins, CAMP-like factor, caseinase, amilase, lipase, lecithinase, mucinase, DNA-ase). The exo-enzymatic profile of bacterial cultures of 2 and 5 hrs proved to be similar, the tested supernatants exhibiting haemolytic activity, and for Staphylococcus aureus, amilase and caseinase activities. Supernatants of and 5 hrs bacterial cultures exhibited also cytotoxic effect on HEp-2 cells. Supernatants of bacterial cultures of 24 hrs exhibited neither enzymatic activities, nor cytotoxic effect on HEp-2 cells, probably due to the inhibition of phenotypic expression of enzymatic activities at high bacterial densities through the activation of the quorum-sensing system. Bacterial supernatants did not significantly influence the HEp-2 cells division rate.