The effects in vitro of both teicoplanin and vancomycin of blood peripheral human neutrophils have been studied by assays of antibiotic uptake and intracellular killing of previously phagocytosed Staphylococcus aureus. The effects of vancomycin and teicoplanin (a novel glycopeptide antibiotic), at the therapeutic concentrations reached in plasma (10, 25, 50, 75 and 100 mg/l) and at different times of incubation (5, 15, 30 and 60 min) were studied. The results indicate that: (1) the bactericidal effect of neutrophils increases with incubation time, (2) in the presence of both teicoplanin and vancomycin, the number of CFU/ml of intraphagocytic S. aureus declines with both increasing incubation time and exposure dose of the antibiotics and (3) at 100 mg/l of teicoplanin there is a significant increase in the percentage inhibition of S. aureus growth at all the times studied.