A model was devised to determine the effects of several foreign bodies (microcrystalline collagen hemostat (MCCH), blood clot, catgut suture) on S. aureus wound contamination and wound infection. In a subinfected wound model, MCCH, when compared with the other foreign bodies, showed an increase in the number of wounds classified as "contaminated," but 84 percent of these wounds yielded bacterial counts below the level accepted for biologically significant wound infection (10 to the 5th power bacteria per gram tissue). The number of "infected" wounds was not significantly greater than the number found in the uninoculated control group. In the infected wound model, all groups of inoculated animals showed significant infections. The severity of the wound infection was unaffected by the presence of catgut suture, clotted blood, or MCCH. Higher levels were not seen for the MCCH animals than for the inoculated control animals. We did not see in these experimental wound studies with MCCH a significant aggravation of wound contamination or wound infection during the 48 hour period following inoculation with varying dose levels of S. aureus. Further studies would be necessary to determine the possible bacteriological response after 48 hours.