We tested the effect of a preparation of human lung lavage surfactant (SAM) on phagocytosis and intracellular killing of Staphylococcus aureus by human alveolar macrophages (AM). When staphylococci were incubated with 100 to 300 micrograms of SAM, AM phagocytosis but not intracellular killing efficiency was enhanced. The mean numbers of intracellular staphylococci/AM were 36.0 +/- 2.7 and 23.3 +/- 2.8 in the SAM and control groups, respectively (p less than 0.001). The AM intracellular killing efficiency was 40.9 +/- 3.3% and 39.5 +/- 3.9% in the SAM and control groups, respectively (p greater than 0.05). Our results suggest that SAM is an important nonimmune opsonin for bacterial phagocytosis by human AM.