This study was performed to ascertain whether a standardized extract from Echinacea angustifolia (Polinacea) affects proliferation and interferon gamma (IFN-gamma) secretion in bovine peripheral blood mononuclear cells (PBMC). PBMC from six Holstein heifers were incubated with 0, 6.3, 20, 60, or 180 microg/ml of the tested compound. Proliferation was stimulated by concanavalin A (ConA) or pokeweed-mitogen (PWM). Secretion of IFN-gamma was stimulated by ConA. All concentrations of Polinacea exerted a mitogenic effect. With respect to control PBMC (0 microg/ml), the lowest and highest increase of proliferation were observed with Polinacea at 6.3 (2-fold increase) or 180 (10-fold increase) microg/ml, respectively. Polinacea at 180 microg/ml reduced ConA-driven proliferation, whereas at 20 and 60 microg/ml improved proliferation of PWM-stimulated PBMC. IFN-gamma secretion was not affected. In conclusion, Polinacea modulates bovine PBMC proliferation, and deserves to be tested in vivo to define conditions that may benefit from its utilization.