We measured the antibody response in 10 victims of acute blunt trauma and penetrating trauma who were immunized against Klebsiella pneumoniae and Pseudomonas species within 72 hours of injury. The two vaccines, which were previously shown to be safe and immunogenic in uninjured humans, were a 24-valent K. pneumoniae capsular polysaccharide vaccine and an eight-valent Pseudomonas O-polysaccharide-toxin A conjugate vaccine. The patients were between 18 and 44 years of age, had Injury Severity Scores that ranged between 9 and 34, and did not have chronic infections or malignancies. On days 14 and 28 after immunization, all patients had a response of greater than fourfold to at least six of the nine Pseudomonas vaccine antigens. Half of the patients responded to eight of the nine antigens. Nine patients responded to at least 18 of 24 Klebsiella antigens, and seven patients responded to 22 of the 24 antigens. No important side effects were attributed to the vaccines. The results of this preliminary study indicate that active immunization against potential pathogens is possible in victims of acute trauma.