Fludarabine (25 mg/m2 for 5 d, every 4 wk, for 6 courses) was administered as first line therapy in 32 symptomatic chronic lymphoproliferative diseases. All CLL patients achieved at least partial response (5 CR, 2 nPR, 9 PR) but 44% of patients relapsed. In LG-NHLs response and relapse rate were similar. Haematological toxicity was low. VDJ rearrangement PCR analysis was performed on marrow samples at diagnosis and at the time of response evaluation. In the 3 patients who underwent high dose therapy with peripheral blood progenitor cell rescue analysis was also performed on apheresis samples and on marrow samples at the end of the procedure. Clonal VDJ rearrangement was always evident after Fludarabine therapy even in those patients who achieved histological and immunophenotypic complete remission, whereas it disappeared in 2 of 3 patients who underwent HDT. Our data confirm that Fludarabine monotherapy can reduce the neoplastic mass to a subclinical level and suggest the possibility that high dose therapy might produce true complete remission.