Using a previously developed guinea pig model of foreign body infection, we examined ultrastructural and functional surface alterations of Staphylococcus aureus strain Wood 46 during the early phase of infection. Exopolymer-free bacteria were prepared and inoculated into subcutaneously implanted tissue cages. After three hours, the bacteria showed abundant capsular and intercellular exopolymers, which were visualized by transmission electron microscopy. Exopolymers were also produced by S. aureus exposed in electron microscopy. Exopolymers were also produced by S. aureus exposed in vitro to fluid from the tissue cage. In contrast, human serum albumin prevented exopolymer production by S. aureus. The influence of exopolymers on the susceptibility of S. aureus to ingestion and phagocytic killing by neutrophils was tested in vitro and found to be negligible. Furthermore, adherence of S. aureus to fibronectin-coated surfaces was unaffected by the presence or absence of exopolymers. Thus, in our experimental model, exopolymers are produced early during the onset of infection, but they have little impact on adherence and phagocytosis.