We present herein the levels of the early markers of blood coagulation activation and TNF-alpha in 12 children with the epidemic form of the hemolytic-uremic syndrome, median age 16 months, range 12-18. All patients recovered from the disease within 2 to 4 weeks. Four blood samples were collected: at admission, 1 week and 2 weeks later and on remission. Prothrombin fragments 1 + 2 (F1 + 2), thrombin-antithrombin complex (TAT) and tumor necrosis factor alpha (TN-alpha) were assayed by commercial ELISA techniques, while von Willebrand factor (vWf) was measured by Laurell's method. At admission, F1 + 2 and TAT levels were 7.8 nM (3.7-12.3) and 22.7 ng/ml (8-76), respectively. Besides, significant correlations were obtained for F1 + 2 levels vs blood creatinine, r: 0.57 p < 0.001; F1 + 2 vs urea, r: 0.66 p < 0.001; TAT vs blood creatinine, r: 0.77 p < 0.001; TAT vs blood urea, r: 0.59 p < 0.001. Median vWf value at admission in 11/12 children was 260% (170-420), correlating with F1 + 2, r: 0.77 p < 0.001 and with TAT, r: 0.41 p < 0.01. Such values tended to normalize with the improvement of the disease. A negative correlation was found for platelet count vs F1 + 2, r: -0.64 p < 0.001. TNF-alpha levels were increased in 5/12 children, 22.2 pg/ml (17.2-53.7). These results may be attributable to similar stimuli on endothelial cells.