Neutrophil ingestion and bactericidal capacity were studied in 35 burn patients. Using Pseudomonas aerudomonas as the test microorganism, it was found that defects in bactericidal capacity were common, particularly in phagocytes of patients with burns greater than 30% of the body surface. Even though reduced neutrophil ingestion was observed in a significant number of assays the incidence was low in comparison to the incidence of reduced bactericidal capacity. Defects in phagocytic function were not detected until at least 5 days after injury and at the time of discharge all patients that were studied had resumed normal phagocytic function.