Seventeen patients (aged 50-85 years) with relapsed or refractory non-Hodgkin's lymphoma (NHL, 10 patients) or chronic lymphocytic leukaemia (CLL, seven patients) were treated with a combination of fludarabine 25 mg/m2/d and cyclophosphamide 250 mg/m2/d for 3 d repeated every 4 weeks. 12 patients had previously received purine analogue therapy of which four had progressive disease during treatment. The overall response rate of patients with CLL was 71% (28% CR, 43% PR) and for NHL was 50% (0% CR, 50% PR). Toxicity consisted of nausea and vomiting which was maximal in the 3 d after therapy, infections and haematological suppression which was prolonged in some patients. This combination, which is based on a rational prediction of synergistic activity, is highly effective but associated with significant problems with tolerance.