The aim of the study was to evaluate the activity and toxicity of cladribine (2-CdA) in combination with cyclophosphamide (CY), the CC schedule, in patients with previously untreated B-cell chronic lymphocytic leukemia (B-CLL). From November 1998 to May 2002 82 patients with advanced or progressive B-CLL received treatment with 2-CdA at a dose of 0.12 mg/kg for three consecutive days and CY at a dose of 650 mg/m(2) on day 1. The cycles were repeated at four week intervals or longer if severe myelosuppression occurred. Guidelines for the evaluation of response and toxicity were those developed by the National Cancer Institute sponsored Working Group. Minimal residual disease (MRD) was detected by immunophenotyping only in patients with CR by standard criteria. In the analysed group an overall response (OR) rate (CR+PR) of 87.8% (95% CI 80.7-94.9%) was achieved, including complete response (CR) in 29.3% patients (95% CI 19.4-39.1%). Twenty-two of 24 patients with CR and 39 of 48 patients with PR are still in remission. Median duration of follow-up in these patients is 11.8 months (range 3-25.4). MRD was only detected in six out of 24 (25%) patients with CR. Grade III/IV thrombocytopenia was seen in four patients (4.9%) and neutropenia in 10 (12.2%). Severe infections were noted in 21 (25.6%) patients. Thirteen patients died, including seven with treatment related toxicity, one because of CLL progression and five because of reasons not related to CLL. In conclusion, the CC schedule is a highly active regimen in previously untreated B-CLL, with acceptable toxicity. The efficacy of the regimen seems to be higher than observed earlier after treatment with 2-CdA alone. A randomized clinical trial is in progress in our institutions.