To examine the effects of peptidyl membrane interactive molecule D4B in a murine model of lethal burn wound infection. Experimental Design: Four experiments were performed: (1)growthinhibitionassaysofPseudomonasaeruginosatreated with D4B, 0 to 100 µmol/L; (2) in vitro coculture of bone marrow cells with D4B, 0 to 100 µmol/L; (3) D4B treatment survival studies after burn injury only or burn wound infection in mice; and (4) peripheral white blood cell count, burn wound tissue bacterial culture, and burn wound morphological analysis at days 1, 2, and 3 after injury. Setting: University medical center laboratory. Subjects: Groups of B 6 D 2 F 1 male mice (20 each) were studied. Interventions: Full-thickness scald burn, 15% of total body surface area, with P aeruginosa topical infection, and subeschar injections of D4B at 200 µg or 0.25 mL of placebo per mouse at 2 and 24 hours after injury. Main Outcome Measures: Animal survival after thermal burn wound bacterial infection, circulating leuko-cyte numbers, in vitro clonal cell culture of granulocytemacrophage progenitor cells, and wound histopathological analysis. Results: The survival rate in the D4B-treated group was nearly 2-fold greater than that in controls (PϽ.01) during 14 days of study. Bacterial quantitative wound cultures disclosed significant reductions in bacterial numbers at days 1, 2, and 3 in D4B-treated animals as compared with controls (PϽ.05 to Ͻ.01). D4B induced a dosedependent inhibition of bacterial cell growth when added to in vitro P aeruginosa cultures (PϽ.01). Granulocytemacrophage progenitor cell growth in culture was not altered by D4B treatment. D4B-treated animals displayed no signs of toxic effects or impairment in wound healing. Conclusions: The peptidyl membrane interactive molecule D4B had the ability to improve survival after gram-negative burn wound sepsis via direct antimicrobial effects. Peptidyl membrane interactive molecules may offer the potential of alternative treatments to standard topical agents or in patients with drugresistant microbes.