Despite some encouraging first results, experience with 2-chlorodeoxyadenosine (CdA) in the treatment of Waldenström's macroglobulinaemia (WM) has not as yet been very extensive. The present paper reports a clinical trial of the use of CdA in 18 patients having previously treated (n = 13) or untreated (n = 5) WM. CdA was administered by continuous intravenous infusion at a dose of 4 mg/m2/day for 7 days (5 patients) or as 2-h intravenous infusions at a dose of 5.6 mg/m2/day for 5 days (13 patients). Partial response was obtained in 7 cases. In this small series, no correlation could be found between response to CdA and patient characteristics at inclusion. During the first course of therapy, grade 4 neutropenia (< 0.5 x 10(9)/L) and thrombocytopenia (< 25 x 10(9)/L) developed in respectively 4 and 6 cases. In comparison with earlier reports haematological toxicity was more severe and the overall response rate lower in the present series of patients.