Aerobic and anaerobic bacterial contamination of scalp wounds, indriven bone fragments, and brain tracks were studied in two groups (A and B) of nonrandomized patients with missile head wounds in a 20-month study of patients from the front lines of the Iran-Iraq war. In the 53 Group B patients, the primary debridements, most of which had been performed within 24 hours after injury, were deemed insufficient and a secondary definitive exploration was performed. Group A patients (62) had primary definitive explorations at Nemazee Hospital after a mean of 66.5 hours since injury. All of the patients had been started on dexamethasone and a combination of either ampicillin and chloramphenicol or crystalline penicillin G and chloramphenicol after field evacuation. The contamination rate of scalp wounds, bone fragments and brain tracks was slightly higher in Group A (38.4%, 22.2%, and 29.6% respectively, for Group A and 31.9%, 19.5%, and 27% for Group B, respectively). Staphylococcus albus among the gram-positive and Acinetobacter among gram-negative bacteria were the most common infecting organisms. Fifty per cent of the bacteria cultured from the brain tracks of Group A and 30.8% of those cultured from Group B patients were gram-negative. A total of 125 patients in four groups was included in our overall study of victims of missile wounds that violated the dura mater. Four patients developed meningitis at Nemazee Hospital (3 postoperatively and 1 after facial penetration). Two patients in Group B were admitted with meningitis (1 with an accompanying abscess), 1 of them 20 days and the other 60 days after exploration at two different centers.(ABSTRACT TRUNCATED AT 250 WORDS)