Ovotransferrin (OTF) is an acute phase protein in chickens, serum levels of which increase in inflammation and infections. To understand the significance of OTF in inflammation, we studied its in vitro effects on HD11 cells, a macrophage cell line, and heterophils isolated from blood using a panel of variables indicative of cellular activation. These included the production of interleukin-6 (IL-6), nitrite, matrix metalloproteinase (MMP), oxidation of dichlorofluorescein diacetate for respiratory burst and the degranulation of heterophils by the loss of fluorescein isothiocyanate positive cytoplasmic granules. The results show that ovotransferrin stimulates the production of IL-6, nitrite and MMP by HD11 cells and augments phorbol ester-induced respiratory burst. Ovotransferrin stimulated heterophils to produce IL-6, and MMP, but failed to produce nitrite, enhanced respiratory burst activity and degranulation. These results suggest that ovotransferrin can modulate macrophage and heterophil functions in chickens.