This study was designed to investigate the immunostimulatory effect of low dose Il-2 treatment in B-CLL patients previously treated with 2-chlorodeoxyadenosine (2CdA) in whom severe depletion of T lymphocyte subsets was observed. Four patients enrolled into the study had previously been treated with 3-6 courses of 2CdA. All patients suffered from recurrent infections and showed CD4+ and CD8+ immunosuppression. Recombinant Il-2 was given subcutaneously at a dose of 100 micrograms (1.8 x 10(6)IU) daily for 6 weeks. The drug was administered between 2CdA courses. These preliminary studies showed a marked increase in T cell subsets after Il-2 treatment. All patients displayed an increase of NK cells and there was increased expression of Il-2 receptors (CD 25 and CD 122) on lymphocytes. It is possible that the combination of cytotoxic therapy with 2CdA and low dose rIl-2 could stimulate the T-cell immune system and may be a promising regimen in patients with B-CLL with severe depletion in T-cell subsets.