We have previously described the protective effect of a lipoidal splenic factor (SF) against lethal endotoxemia in mice. Since this protective effect is also accompanied by significant antithrombotic changes, and since burn injury causes thrombosis and consumptive coagulopathy, it was postulated that SF decreased the severity of the burn wound. Swiss white mice were anesthetized with pentobarbital sodium and then burned on a depilated area of the lower back with a 2-cm diameter stainless steel weight at 95° for 10 sec. SF (10 mg/ kg) (n= 20) or an equal volume of saline (controls) (n= 13) was administered within 1 hour after thermal injury. Severity of burn injury was assessed by examination of hematoxylin and eosin-stained biopsies obtained 24 hours postburn by a grading scale of 0 (normal) to 4 (severe) depending on the degree of epidermal loss, coagulation necrosis, and inflammatory cell infiltrate. Average degree of burn severity was 1.10 ± 0.20 for SF recipients and 2.85 ± 0.27 for the controls (p < 0.001).