&NA;Of the several tests which measure leukocyte bactericidal competency only one, chemotaxis, has been reported to reflect both leukocyte dysfunction and patient mortality in major thermal injury. To validate the reliability that chemotaxis reflects mortality functional chemotactic index (FCI) was measured in leukocytes from 33 patients with 30% or greater total body surface area burns. Additionally, nitroblue tetrazolium (NBT) reduction and O2consumption were compared to FCI. Significant decreases were seen in FCI values compared to normals. No differences, however, were seen in FCI values between surviving and nonsurviving patients. NBT reduction and O2consumption also showed decreases with a significant difference between the mean decrease in surviving and nonsurviving patients. While the data show all these laboratory tests to be reflective of significant impairments in host defense, they do not appear to be reliable as predictive indices of patient survival and therefore should not be interpreted as such.