An animal model involving the subcutaneous implantation of tissue cages into guinea pigs and subsequent infection with Staphylococcus aureus was used for study factors pertinent to foreign body infection. Whereas 10(8) colony-forming units (cfu) of S. aureus strain Wood 46 did not produce any abscesses in the absence of foreign material, 10(2) cfu was sufficient to infect 95% of the tissue cages despite the presence of polymorphonuclear leukocytes (PMNLs) in sterile tissue cage fluid. Opsonization of S. aureus by tissue cage fluid was adequate during the first hour of infection, but opsonic coating of the organisms decreased at 20 hr after the induction of infection. PMNLs from sterile tissue cage fluid showed decreased phagocytic and bactericidal activities when compared with PMNLs from either blood or peritoneal exudate obtained after short- or long-term stimulation (P less than 0.001).