The serum concentrations of circulating ICAM-1 (cICAM-1) and soluble receptors for interleukin-2 (sIL-2R) were evaluated on 48 patients with B-cell chronic lymphocytic leukaemia (B-CLL) and on 15 healthy control subjects. The mean +/- SD concentration of cICAM-1 was significantly higher (p < 0.002) in B-CLL patients (407.7 +/- 164.3 ng/ml) than in healthy controls (245.4 +/- 76.7 ng/ml). Patients with progressive disease had higher cICAM-1 levels than patients with "indolent" disease (440.38 +/- 32.3 ng/ml versus 321.36 +/- 14.45 ng/ml; p < 0.0001). Serum levels of cICAM-1 were also significantly higher (p < 0.0002) in patients with advanced stage (III-IV) than in those with early stage (I-II). The increase of cICAM-1 levels was positively correlated to increases of soluble receptors for interleukin-2 (r = 0.9; p < 0.0001). These results seem to show that the measurement of serum levels of cICAM-1 may be an useful tool for monitoring disease activity and tumoral mass in patients with B-CLL. However, further studies are needed to define the functional role of high cICAM-1 levels in the immunological dysregulation of patients with malignancy.