A randomized prospective double-blind study of thymopentin was performed upon 24 severely burned patients to evaluate its efficacy in correcting postburn immunologic abnormalities and preventing infectious morbidity and mortality. Patients in the treated group received 50 milligrams of thymopentin daily for the first two weeks after injury and three times weekly thereafter until the patient was no longer at risk for having infections develop. The placebo group received saline solution intravenously. The rate of infectious complications was recorded. Immunologic tests used at least weekly were: white blood cell counts, OKT4 to OKT8 ratios, lymphocyte blastogenesis and neutrophil bactericidal index. There were no differences noted in patient mortality, infectious complications or antibiotic use. There were two significant differences noted among the immunologic tests. First, there was a decreased lymphocyte blastogenic response in the treated group at two weeks after injury without a difference in T4 to T8 ratios. Second, there was less leukopenia during the first week after injury in the treated group.