A model of experimental post-traumatic osteomyelitis is described in which the femur of guinea pigs was fractured and infected with E. coli (10(5)) or Staphylococcus aureus (10(4)). Traumatized uninfected animals served as controls. The animals were further divided within each group by treating the fractured site with an intramedullary wire in one half. Osteomyelitis developed and became chronic in all guinea pigs infected with Staph. aureus, and in nine of 12 infected with E. coli. All animals infected with E. coli treated with an intramedullary wire developed chronic osteomyelitis; only four of seven from E. coli-infected animals with fractures developed this disease. Moreover, Staph. aureus could be recovered from the osseous tissue in the chronic stage of the disease regularly, while E. coli was only present in the early weeks after operation, but not in the chronic stage.