The contents of nitric oxide (NO) in the blood were measured by electron spin resonance (ESR) method in Wistar rats with 35% TBSA III degrees burn. NO is endothelium derived relaxing factor (E-DRF) released by vascular endothelial cells. The results showed that: 1. Blood NO contents were not found to be significantly increased (72 hours postburn); 2. Escherichia coli lipopolysaccharide (LPS, endotoxin) could induce excessive NO formation in early burns.