Preliminary results indicate that inhibitors of the nuclear enzyme topoisomerase (topo) I, such as topotecan, may be active in non-Hodgkin's lymphoma (NHL). Pre-clinical studies have shown sequential administration of a topo I and II inhibitor has supra-additive anti-tumor effects in some model systems, and that greater cytotoxicity occurs if the topo I inhibitor is given first. We enrolled, 22 eligible patients with relapsed or refractory intermediate grade NHL in a phase II study ofsequential administration of topotecan 1.25 mg/m2 days 1-5 and etoposide 50 mg po b.i.d. days 6-12, every 28 days without G-CSF. Most patients had diffuse large B-cell lymphoma and all had received only one prior regimen (CHOP, 20 patients, or equivalent, 2 patients). Patients with stable or responding disease were allowed to proceed to high-dose therapy and autologous stem-cell transplant after 2 cycles of therapy. The 22 patients received a total of 62 cycles of topotecan + etoposide (median 2, range 1-6), and 4/22 completed all six planned cycles. Hematologic toxicity was significant and resulted in incomplete etoposide dosing in half of all cycles in 16/22 patients. Nineteen of twenty-two patients had grade 3/4 neutropenia, 12 had grade 3/4 thrombocytopenia, and 6 grade 3/4 anemia. Eleven patients had at least one episode of febrile neutropenia or had documented infection. Non-hematologic toxicity was mild. Four patients had a partial response (PR) (18.2%), nine had stable disease and seven progressed; three patients with stable disease went on to ABMT. The combination of topotecan and etoposide as given in this study has modest activity in relapsed/refractory aggressive histology NHL, and produces marked myelosuppression. Other doses and schedules combining topo I and II inhibitors, or topo I inhibitors with alkylating agents, should be explored with the addition of hematopoietic growth factors in this patient population.