With use of a quantitative limulus assay, the levels of circulating endotoxins were examined in a population of burn patients with injuries covering 1% to 88% of the total body surface area (TBSA). In cases in which the injury was less than 20% TBSA, the increases in endotoxins were only 35% as compared with those of normal controls. As the extent of injury increased, the levels of endotoxins also increased: burns between 21% and 40% TBSA showed average increases of over 350% and burns in excess of 40% showed increases of 500%. The relationship between burn size and total endotoxin burden was significant (p = less than 0.01). Time-course studies indicated that in most cases, peak endotoxin levels occurred 3 to 4 days after injury. The data also showed that there was no relationship between the age of the patient and the extent of the endotoxin increase.