Bacteriological studies were performed on 45 craniocerebral missile wounds incurred in Vietnam within 2 to 4 hours of occurrence. All missiles had penetrated into the brain. Aerobic and anaerobic cultures were taken of the skin wound, brain, and indriven bone fragments. Forty-four of the skin wounds were contaminated, predominantly with staphylococcus. Only five brain wounds showed bacterial contamination 2 to 4 hours after wounding, indicating that many missile tracks within the brain are initially sterile. Of the patients who had early debridement, 45% had contaminated bone within the brain; possibly up to 75% of all indriven bone chips were sterile. The authors draw the following conclusions. Complete brain debridement with removal of all indriven bone is ideal. Accessible retained bone should be removed by reoperation. Multiple reoperations for an inaccessible retained fragment are inadvisable, however, as fatalities or severe neurologic residua may result. An individual indriven bone chip has a small likelihood of bacterial contamination provided initial debridement was done early. This knowledge may justify an expectant policy in certain individuals harboring an inaccessible retained bone fragment. The retained fragment would be removed only if untoward difficulties develop.