Wound healing and granulation tissue fromation can be accelerated by inoculation with live pathogenic microorganisms. For further elucidation of this phenomenon the present work was undertaken to study the effects of Staphylococcus aureus microorganisms on the inflammatory reaction and blood flow in developing granulation tissue in rats. Cylindrical hollow sponge implants were used as an inductive matrix for the growth of granulation tissue. In control animals 1 ml of wound fluid was withdrawn from the central dead space of the implant immediately after implantation and replaced with 1 ml of physiological saline. In experimental animals the implants were injected with live staphylococci, 102 or 105 microorganisms/ml. Wound fluid was analyzed 3, 7, 10 and 14 days after implantation, whereas measurements of local blood flow and albumin extravasation in the granulation tissue were made after 7 days. Implants inoculated with 105 organisms developed infection with pus formation while implants contaminated with 102 organisms showed no infection. In wound fluid specimens collected from the infected implants correlation between the number of polymorphonuclear leukocytes and prostaglandin E2 concentration was statistically significant. The most prominent finding in contaminated but uninfected implants was an enhanced local blood flow. This may explain some of the mechanisms leading to S. aureus-induced acceleration of wound healing.