Liposomal daunorubicin (DaunoXome) was substituted for doxorubicin in the CHOP regimen, aiming to reduce toxicity and maintain or improve efficacy in elderly patients. Eligibility criteria included: age >or=60 years; previously untreated aggressive non-Hodgkin Lymphoma (NHL) and performance status (PS) 0-2. Treatment was cyclophosphamide 750 mg/m(2), vincristine 1.4 mg/m(2) (maximum 2 mg), and DaunoXome 100 mg/m(2) i.v. on day 1, prednisolone 100 mg po on days 1-5 and G-CSF 5 microg/kg/day sc, for 6-8 cycles. For the 51 patients, median age was 70 years (range 60-88), 94% had diffuse large B-cell lymphoma (DLBCL) and 55% were high-intermediate or high-risk according to the age-adjusted international prognostic index. A mean of 6 cycles was delivered, with dose reductions of DaunoXome in 8.3% of cycles. The combined CR and CRu rate was 65.2%, survival was 566 days and 5-year survival 35%. Three deaths occurred during treatment and may have been related to COP-X. Only 4 (7.8%) of the remaining patients had >or=10% reduction in LVEF. However, 35% of patients were hospitalised during treatment, mostly for febrile neutropenia. The response rate to COP-X was similar to that expected with CHOP, with low cardiac toxicity. The high rate of infectious complications suggests that the DaunoXome dose used may be too high for this patient group. These results support further investigation of this regimen in patients with aggressive NHL.