A multidrug-resistant Pseudomonas aeruginosa (r-Pa) was isolated from a lethal case of sepsis in a bone marrow transplant recipient. Genotypic analysis of P. aeruginosa isolates demonstrated that sepsis was secondary to gut colonization. The interactions between r-Pa and patient's neutrophils were studied. The results indicate that: (1) the patient's neutrophil killing activity and nitric oxide production against r-Pa or drug sensitive P. aeruginosa (s-Pa) were profoundly impaired; (2) r-Pa cells, but not s-Pa cells or their filtered culture supernatants, induced necrosis of healthy donor neutrophils. Neutrophil necrosis emerges as a remarkable event in the pathogenesis of P. aeruginosa sepsis.