Enhanced levels of soluble TNF-receptors (sTNF-R) have been reported in patients with chronic renal failure. The aim of the present study was to evaluate the effects on sTNF-R levels in plasma of haemodialysis patients of the anticoagulation method and of the type of membrane used, as well as the variability of predialysis sTNF-R levels during time. All haemodialysis patients tested (n = 35) showed increased levels of both sTNF-R55 (72.4 +/- 5.7 ng/ml, P < 0.001) and sTNF-R75 (18.2 +/- 2 ng/ml, P < 0.001) before dialysis, as compared with normal healthy controls (< 2.5 ng/ml for both sTNF-R), confirming previous observations. sTNF-R levels were determined before and during haemodialysis at different time intervals in patients receiving either heparin (2500 U, 5000 U, or 10,000 U), low molecular weight heparin, or periodic saline flushing to prevent coagulation of the extracorporal circuit. A transient, small decrease in both sTNF-R levels occurred at the beginning of haemodialysis (t = 15 min) with all anticoagulation methods used. At the end of haemodialysis, sTNF-R55 and sTNF-R75 concentrations were only minimally affected (P > 0.05). Predialysis sTNF-R levels were similar in patients dialysed on either cellulose diacetate or polyacrylonitrile. Finally, there were only minimal variations in predialysis sTNF-R levels in individual patients during the 1 week observation period. Although the biological consequences of the increased TNF-binding ability of serum from haemodialysis patients is still unclear, it could play a role in the complex immunological perturbations of uraemic patients.