Fifteen patients with B-cell chronic lymphocytic leukemia (B-CLL) have been treated with alpha 2b-interferon (alpha IFN) for one year (3 mega units subcutaneously three times a week). The hematological response and the modulation of immunophenotype, serum levels of soluble interleukin-2 receptor (sIL-2R) and tumour necrosis factor (TNF) have been monitored. Hematologically 67% of cases were classified as responders, although no complete responses were observed; three cases progressed during treatment, and two patients showed stable disease. Both peripheral lymphocytes and CD24+ cell absolute number significantly decreased after twelve months of IFN treatment (40.7 +/- 17 x 10(9)/l versus 15.8 +/- 6 x 10(9)/l, mean values +/- sd, p < 0.01, and 30.4 +/- 5.5 x 10(9)/l versus 8.1 +/- 2.8 x 10(9)/l, p < 0.05, respectively), while CD24+ cell percentage did not change (72.1% +/- 4.6 versus 67.5% +/- 8.8, p not significant). In the majority of cases myelomonocytic markers (CD11c, CD14, CD11b) transitorily decreased during the treatment. Serum sIL-2R levels, elevated in all cases before IFN treatment, increased in responders. Serum TNF levels decreased in patients showing high values before the treatment. The explanation of these findings and their possible implication are discussed.