Despite improvements in immunosuppression, rejection occurs in 50% of liver transplant patients and may cause significant morbidity. The most frequent cause of death after liver transplantation is severe infection. Determination of the cytokine network may lead to earlier detection of patients at risk for severe rejection and infection. For this purpose, 81 patients with 85 liver transplants were monitored for cytokines and neopterin on a daily basis. During the first postoperative month, 28 patients (34.6%) developed acute rejection; 14 patients were successfully treated with methylprednisolone (steroid-sensitive rejection), while 14 patients required additional treatment with FK506 and OKT3 (steroid-resistant rejection). Ten patients developed severe infections, and 11 patients experienced asymptomatic cholangitis. Patients with an uneventful postoperative course (n=37) were the control group. One-year patient survival was 88.9%: 1 patient died because of chronic rejection and Pseudomonas urosepsis; a further 4 patients died of aspergillus pneumonia and bacterial sepsis. Soluble TNF-RII, sIL-2R-, and IL-10 levels were significantly elevated 3 days prior to or at the onset of acute steroid-resistant rejection (P < or = 0.01 versus steroid-sensitive rejection and on uneventful postoperative course). An increase in IL-8, neopterin, and sTNF-RII was indicative of severe infection 3 days prior to onset of infection. In this group of patients, a simultaneous increase in IL-10 indicated a lethal outcome of severe infection. During the second week of acute steroid-resistant rejection and lethal infection, a significant rise in IL-1beta, IFN-gamma, and IL-6 was observed (P < or = 0.01 versus control groups). The different patterns in neopterin- and cytokine-increase could differentiate between severe rejection and severe infection. Furthermore, the increase in these parameters indicated severe rejection--i.e., steroid resistance at the onset of acute rejection--which could prompt us to initiate rescue therapy immediately. The ability to detect patients at risk for severe or lethal infection may result in intensified infectious screening and more aggressive antiinfectious treatment. Therefore, routine monitoring of these parameters may lead to changes in therapeutic management of severe acute rejection and infection after liver transplantation.