A polyvalent Pseudomonas vaccine has been given to 96 consecutive patients who survived the initial five days after admission with burns greater than 20% (average, 42.8%). Death from Pseudomonas sepsis occurred in three (3.1%). In contrast, 11 (14.1%) of 75 similar consecutive patients during the period immediately preceding use of the vaccine died from Pseudomonas sepsis. In the most susceptible groups of patients (those with a 40% or greater burn), mortality from all causes in vaccinated patients was reduced 15.7%, and mortality from Pseudomonas sepsis was reduced 86.0% Minor local reactions to the vaccine occurred in the majority of patients, but there were no serious reactions in over 1,500 injections. This vaccine represents a significant advance in the management of the seriously burned patient, and its use has resulted in a significant decrease in mortality following burn injury.