[en] We measured the soluble (s) receptors CD23, CD8, CD4, interleukin-2 receptor (IL-2R, CD25), and transferrin receptor (TfR, CD71), in normal serum and in patients with chronic lymphocytic leukemia (CLL) and evaluated them in relation to clinical and biological parameters of the disease, as well as serum immunoglobulin E (IgE). Compared to 31 normal individuals, 42 CLL patients had increased levels of sCD23 (98.4 +/- 127.7 versus 0.9 +/- 0.3 U/ml, p < 0.001), sIL-2R (6080 +/- 7030 versus 1420 +/- 640 pg/ml, p < 0.001), sTfR (12,100 +/- 11,250 versus 5000 +/- 1050 ng/ml, p < 0.001), and sCD8 (510 +/- 191 versus 234 +/- 89 U/ml, p < 0.001), but normal sCD4 levels. Mean sCD23 levels remained normal in patients with non-Hodgkin's lymphoma (other than small lymphocytic), Hodgkin's disease, hairy cell leukemia, acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), multiple myeloma, or solid tumors. Advancing Rai clinical stage was associated with a progressive elevation of sCD23 (p < 0.001), while sCD8 (p < 0.05), sIL-2R (p < 0.001), and sTfR (p < 0.005) were highest in stage 2 patients. Discriminant analysis confirmed the value of soluble receptor determinations in the clinical evaluation of CLL patients. sCD23 correlated with sIL-2R (p < 0.001) and sTfR (p < 0.05) but not with sCD4 or sCD8, and displayed an inverse relationship with serum IgE (NS) and total gamma-globulin (p < 0.05). sIL-2R correlated with sCD23 (p < 0.001), sTfR (p < 0.001), sCD4 (p < 0.01), and sCD8 (p < 0.01). The lymphocyte count correlated with serum lactate dehydrogenase (LDH) (p < 0.05), sCD23 (p < 0.001) and sIL-2R (p < 0.01) but not sTfR, sCD8, or sCD4. Chemotherapy produced consistent reductions of sCD23 levels in two responding patients. We conclude that: (i) sCD23 is considerably elevated in CLL, correlates with the tumor mass and clinical stage, and could be helpful in monitoring these patients; and (ii) sIL-2R, sCD8, and sTfR levels are less specifically increased and could be influenced by other factors such as immune activation and erythropoiesis.