Enhanced concentrations of soluble forms of the receptor for tumour necrosis factor (TNF)-alpha have been detected in the serum of cancer patients. We determined serum concentrations of soluble TNF receptor p55 (sTNF-R55) in patients with haematological neoplasias, 50 patients suffering from non-Hodgkin's lymphoma (n = 35), Hodgkin's disease (n = 10) and multiple myeloma (n = 5). Compared with healthy controls and with patients with potential thyroid disease, significantly elevated concentrations of sTNF-R55 were found (mean +/- standard error: 2.68 +/- 0.22 vs. 1.23 +/- 0.21 ng/ml, P < 0.0001 and 2.18 +/- 0.32 ng/ml, P = 0.03). Likewise, neopterin concentrations were raised (19.6 +/- 3.66 vs. 5.3 +/- 0.25 nmol/l in controls, P < 0.0001). We found a significant correlation between sTNF-R55 and neopterin concentrations (Rs = 0.544, P < 0.001). Patients with weight loss showed higher sTNF-R55 concentrations than patients with stable weight. Our results confirm the relevance of sTNF-R55 concentrations in serum of patients with cancer.