Interleukin-2 (IL-2) promotes multisystem organ edema, lung neutrophil sequestration, and platelet activation through alterations in the microvascular barriers and permeability. IL-2, complement, platelet, and vascular endothelial activation were evaluated in 60 patients. One-factor analysis of variance indicated a significantly increased absolute neutrophil count on day 1 (p < 0.0001) and decreased C1Inh, p = 0.0001, with elevated IL-2 levels in the 20% to 40% group (p = 0.008). Endothelin-1 levels were significantly increased in the 20% to 40% total body surface area group on day 5. The absolute neutrophil count was significantly reduced in both groups, and C1Inh rose to near normal levels by day 5. No significant elevations of 6-keto prostaglandin F1 alpha were observed on day 1 or day 5 in the < 40% total body surface area group; however, these levels were significantly elevated on day 1 in the > 40% total body surface area group. Thromboxane B2 and platelet factor 4 were significantly elevated in all groups (p = 0.001) on days 1 and 5. Regression analysis implicated infection as a significant contributor to the IL-2 variations (r2 = 0.61), with inhalation injury minimally affecting IL-2 plasma levels (r2 = 0.09). Generalized edema increased with increasing burn wound size in parallel with elevated IL-2 and endothelin-1 levels, reduced C1Inh levels, and leukocytosis in the first week after thermal injury. These data suggest that there are dynamic interactions among the endothelium, cytokine stimulation, leukocytosis, complement, and platelet activation in promoting the microvascular permeability.