The cytokines tumor necrosis factor-alpha (TNF-alpha) and its soluble TNF receptors 55 and 75 (sTNFR55, sTNFR75), interleukin-1 beta (IL-1BETA) and interleukin-6 (IL-6) were measured in plasma from 13 patients with the hemolytic uremic syndrome (HUS) on admission. No significant changes in the plasma levels of TNF-alpha and IL-1beta were detected in the HUS patients as compared to the plasma levels of the control groups. Levels of IL-6 were significantly elevated in the plasma of those HUS patients who had external manifestations, consisting of seizures, loss of consciousness, coma and pancreatic necrosis. Although the exact function of IL-6 in the plasma of HUS patients is still unknown and the group of HUS patients is small, plasma IL-6 is associated with the the severity and outcome of the disease. Plasma levels of sTNR55 and sTNFR75 were significantly elevated in all HUS patients compared to the healthy controls, but they were also elevated in the children with chronic renal failure. This indicates that elevated levels of circulating sTNFR should be carefully interpreted when kidney failure exists.