The purpose of this study was to compare the in-vitro effects of a European-based formocresol formulation that incorporates eugenol with formocresol alone on the adhesion of macrophages to plastic surfaces.Macrophages were obtained from Wistar rats. The adherence capacity of macrophages to a plastic surface was determined. Assays were carried out in Eppendorf tubes incubated for 15 min at 37 degrees C in a humidified atmosphere of 5% CO2. The adherence index was calculated.Results showed that both formocresol/eugenol and formocresol alone significantly decreased the adherence index of macrophages. The formocresol formulation that incorporated eugenol was more potent in inhibiting macrophage adhesion than formocresol alone.Taking into account that adherence to a substrate is the first step in the phagocytic process of macrophages and in antigen presentation, both formocresol formulations could inhibit macrophage function and modulate immune and inflammatory responses in dental pulp and periapical tissues.