OBJECTIVE A phase I and pharmacologic study to evaluate the feasibility of administering paclitaxel (PTX) in combination with topotecan (TPT) without and with granulocyte colony-stimulating factor (G-CSF) in women with recurrent or refractory ovarian cancer. METHODS TPT was administered as a 30-minute infusion daily for 5 days and PTX was given as a 24-hour infusion (PTX-24) either before TPT on day 1 or after TPT on day 5. Each patient received both schedules on an alternating basis every 3 weeks. Sequential dose escalation of TPT or PTX-24 without and with G-CSF resulted in five dosage permutations of TPT/PTX (mg/ m2): 0.75/135 without G-CSF and 0.75/135, 1.25/135, 1.50/135, and 1.25/170 with G-CSF. RESULTS Twenty-two patients received 109 courses of therapy. Dose-limiting myelosuppression consistently occurred at the first TPT/PTX-24 dose level (0.75/135 mg/m2) in the absence of G-CSF support. Although the addition of G-CSF resulted in reduced rates of complicated neutropenia, the incidences of dose-limiting neutropenia and thrombocytopenia were unacceptably high after the doses of either TPT or PTX-24 were increased. Paired analysis showed similar hematologic toxicities between the two sequences of drug administration. The pharmacologic behavior of both TPT and PTX-24 was not altered by drug sequencing. Major antitumor responses occurred in 40% of patients with measurable and assessable disease, including 45% and 9% of patients with potentially cisplatin-sensitive and -resistant tumors, respectively. CONCLUSIONS The recommended doses of TPT on a daily times-five schedule combined with PTX-24 in these patients were 0.75 mg/m2/d and 135 mg/m2, respectively, with G-CSF support. Although this dose of PTX has significant single-agent activity in ovarian cancer, the dose of TPT is much lower than the TPT dose at which single-agent activity has been observed. Due to the inability to administer near relevant single-agent doses of both drugs in combination, as well as the requirement for G-CSF support, further evaluations of this regimen in women with refractory or recurrent ovarian cancer are necessary before it can be recommended for previously treated patients in this setting.