The objective of this study was to determine whether phagocytic capacity and opsonic activity in blood and mammary secretions of sows are impaired at parturition compared with later on during lactation. The study comprised eight primiparous sows (Landrace x Yorkshire) free from clinical signs of disease. Blood and mammary secretion samples were collected within 48 h of parturition and 7 and 16 days after parturition. Numbers and proportion of polymorphonuclear neutrophils (PMN) were determined in blood and mammary secretions. Phagocytic capacity was assessed in whole blood and in a cell suspension derived from mammary secretions. Opsonic activity was assessed in serum and i cell-depleted, skimmed mammary secretions. The two assays were based on chemiluminescence, both having zymosan and Escherichia coli as target particles. Numbers and proportion of PMN in mammary secretions were higher (P < 0.05) at parturition than later on during lactation. A parturition, phagocytic capacity in cell suspensions derived from mammary secretions was higher for both (P < 0.05) and E. coli (P < 0.1). However, when phagocytic capacity was related to the number of PMN in the suspension no such difference was observed. The opsonic activity in cell-depleted, skimmed mammary secretions at parturition was lower (P < 0.05) for zymosan but not for E. coli. None of the described variations were reflected in blood or serum. The findings of this study do not unequivocally support the theory that an immune suppression at parturition in the sow can help explain the increased incidence of coliform mastitis at that time.