In war, uncomplicated penetrating injuries to limbs require evacuation to a surgical facility. A delay is inevitable between injury and definitive surgical treatment. This paper describes an experimental model that has been developed to assess the efficacy of antibiotics in such war wounds; the aim is to develop a treatment protocol to prevent the development of infection before casualties reach a surgical facility. The model is described in detail. Its use to determine efficacy of an antibiotic regimen, and the consequences of delay in the initial administration of antibiotic, are summarized. Streptococcus Lancefield Group L (Strep L) is a pig pathogen analogous to the Streptococcus pyogenes Lancefield Group A in man. The latter is perceived as a major threat to the casualty with a neglected penetrating wound. Strep L caused reproducible infection in a low-energy-transfer fragment wound to a pig thigh. When the wound was observed over a period of 7 days, the only other organisms that appeared consistently were pig pathogenic and nonpathogenic staphylococcal species. Despite the site of the wound, fecal organisms were not observed to colonize the wound significantly, neither were they a cause of early wound infection. The treatment regimen studied as benzylpenicillin, 1 megaunit (6 hourly), given intramuscularly. When commenced 1 hour after wounding, this prevented wound infection for 3 days, when Strep L was deliberately inoculated at the time of wounding. If the start of antibiotics was delayed until 6 hours after wounding, antibiotic regimen was less effective; the wound track remained infected at 3 days. In a further series of experiments, Staphylococcus hyicus, a potential pig pathogen (which is penicillin resistant through beta-lactamase production), was introduced in addition to Strep L. The antibiotic regimen remained effective when the Strep L plus 10(3) S. hyicus were inoculated. When 10(4) S. hyicus were introduced, treatment was less effective, but still of some benefit. Inoculation of > 10(5) S. hyicus rendered treatment commencing at 1 hour ineffective. If the start of treatment was delayed to 6 hours after injury, this treatment regimen was adversely affected by the introduction of only 10(3) S. hyicus. In conclusion, an intramuscular benzylpenicillin regimen, commenced 1 hour after wounding, can prevent infection in penetrating soft tissue missile wounds for up to 3 days. A delay of 6 hours renders treatment ineffective.