Wound and blood cultures were obtained from 30 US marines with severe combat-inflicted extremity injuries. On admission to the hospital, the predominant organisms isolated from the wounds were gram-negative bacteria belonging to the Enterobacter and Mimeae groups, Escherichia coli, and Klebsiella. By the fifth hospital day, a significant increase in the number of wounds yielding Pseudomonas and Proteus organisms was noted. Twelve of 30 patients developed positive blood cultures. Enterobacter and Mimeae were most frequently cultured from the bloodstream. In eight instances, the same strain of gram-negative bacteria was isolated from the wounds and blood. Three patients died in gram-negative septicemia. Recommendations for initial antibiotic therapy in severely wounded patients in a combat area are presented.