Impairment of T-cell function is a consistent observation in burned patients. Concomitant with this impairment is an increase in serum factors which inhibit interleukin-2-mediated T-cell functions. These factors are heat labile and do not behave like endotoxins. Nonetheless, treatment of burned patients with endotoxin-neutralizing regimens of polymyxin B reduces the levels of these factors, suggesting that they are generated in response to endotoxin exposure. In addition to factors which inhibit I1–2 responses burn serum contains increases of circulating soluble, cell-free I1–2 receptors. However, the level of I1–2R is not altered by polymyxin B treatment and does not appear to be a direct result of endotoxin exposure. These observations suggest that multiple causes contribute to T-cell impairment in burned patients.