In addition to its biophysical functions, surfactant plays an important role in pulmonary host defense. In this investigation we studied the influence of various commercially available surfactants on the phagocytosis of bacteria that are common pathogens in the neonatal period. Group B streptococci (GBS), Escherichia coli and Staphylococcus aureus were cultured with isolated human polymorphonuclear leucocytes (PMN) and non-specific serum in the presence or absence of different modified natural (Curosurf, Alveofact, Survanta) or totally synthetic, protein-free surfactant preparations (Exosurf, Pumactant). Prior to and after 30 and 60 min of incubation with PMN at different surfactant concentrations (1, 10 or 20 mg/ml), the number of viable bacteria was determined by colony counting. Killing of S. aureus by PMN was not influenced by any of the surfactants. Alveofact and Curosurf had no significant negative impact on phagocytosis. At 20 mg/ml, Curosurf even reduced the number of viable E. coli. Survanta at 10 and 20 mg/ml and Exosurf at all concentrations impaired the killing of non-encapsulated GBS and E. coli. Pumactant at 1-20 mg/ml interfered with the phagocytosis of E. coli. In further experiments we demonstrated that Curosurf did not interfere with the phagocytosis of an encapsulated GBS-strain opsonised by a specific antiserum either. In additional experiments we analysed the influence of the different surfactants on the release of reactive oxygen metabolite by PMN and found that the changes in nitroblue tetrazolium reduction did not necessarily correlate with the findings of the studies on killing. In conclusion, we found that killing by PMN was influenced by the bacterial species and the composition and concentration of the different surfactant preparations. The strongest impairment in phagocytic function of PMN was observed with the protein-free synthetic surfactant Exosurf, a phospholipid preparation that contains the alcohols hexadecanol and tyloxapol as spreading agents.