The purpose of the study was the determination of the activity of the neutrophils isolated from a physiologically sound (non-inflamed) uterus 2 days after ovulation, and comparison of this activity with that of the polymorphonuclear leucocytes (PMNs) obtained from an uterus which had undergone experimentally induced specific or non-specific inflammatory reaction. The study was carried out on 20 cows between the 2nd and the 8th day after ovulation. Activity of PMNs was determined on the basis of the per cent of these cells with Fc receptors for IgG on their surface, and on the basis of assessment of the phagocytic activity. The Fc receptors were determined by the rosette test. The phagocytic activity of PMNs was determined in relation to two standard strains of S. aureus Smith which were phagocytized by mediation of Fc receptors and S. aureus 305 phagocytized by mediation of the "non-immunological" receptors. The study showed that the inflammatory process in the uterus caused intensive migration of large numbers of PMNs into the lumen. These PMNs have their properties altered: there is a significantly lower per cent of cells with Fc receptors in this cell population and lower Fc-dependent phagocytic activity. A significant rise in the phagocytic activity mediated by non-immunological receptors occurs at the same time in this cell population.