We undertook a prospective study to evaluate the role of the combination of fludarabine and cyclophosphamide in patients with low-grade non-Hodgkin's lymphoma. Twenty-seven patients with low-grade non-Hodgkin's lymphoma were treated with i.v. fludarabine (30 mg/m ) and cyclophosphamide (250 mg/m ) on days 1-3. Cycles were given at 4-week intervals for a maximum of six courses. Fourteen patients (52%) were previously untreated, 13 patients (48%) had been treated with at least one chemotherapy regimen before. Of the 27 patients, 11 (41%) obtained a complete and 13 (48%) a partial remission, thus the overall response rate was 89%. The remission rate in untreated patients was slightly higher than in pretreated patients (93 versus 85%). The toxicity was mild, no treatment-related mortality occurred. Neutropenia was the most common side effect, grade 4 neutropenia of rather short duration was observed in less than 7% of the cycles. At the end of the treatment, the mean CD4 count was 155/ l and the mean CD8 count 204/ l. Severe infections did not occur. These results show that the combination of fludarabine and cyclophosphamide in the doses used in this study is an effective regimen with manageable toxicity in low-grade non-Hodgkin's lymphoma.