Serum levels of tumour necrosis factor-alpha (TNF-alpha) have been evaluated in the peripheral blood of 91 patients with B-cell chronic lymphocytic leukaemia (B-CLL), and have been correlated with the clinical stage (according to Rai's staging system) and relevant haematological and immunological data. Increased values were detected, compared to 36 normal age-matched controls (36 pg/ml +/- 5 versus 0.11 pg/ml +/- 0.08; P < 0.05). An increase of TNF-alpha serum levels was observed in all stages including stage 0, with a progressive increase in relation to the stage of the disease. A significant relationship between serum TNF-alpha levels and the number of circulating monocytes (P < 0.002) and an inverse correlation with the level of the haemoglobin (P < 0.001) was established, as defined by the Pearson's correlation test. In contrast, no correlation was observed between TNF-alpha serum levels and the other parameters taken into account, including the white blood cell and platelet counts, the absolute number of peripheral blood (PB) lymphocytes, CD5+ B lymphocytes, CD57+ lymphocytes, serum levels of lactic dehydrogenase, total serum immunoglobulins and the serum levels of IgG, IgA and IgM. These data suggest that, in addition to the B-CLL neoplastic cells, the PB monocytes may be involved in the release of TNF-alpha.