BACKGROUND Paclitaxel (Taxol) and ifosfamide are among the most active single agents for the treatment of non-small-cell lung cancer. We undertook this phase I dose escalation study to determine the maximum tolerated doses of these drugs which could be administered without growth factors to untreated patients with tumours of this type. METHODS Forty patients with advanced non-small-cell lung cancer were treated with a 3-hour infusion of paclitaxel and a 1-hour infusion of ifosfamide every 3 weeks. Groups of 3 patients were entered at escalating dose levels in traditional phase I design. Starting doses were paclitaxel, 100 mg/m2, and ifosfamide 3 g/m2, and all patients received premedication with dexamethasone, diphenhydramine and a 5-HT3 blocker. Dose escalation occurred only after full toxicity assessment for 2 cycles for all patients in the dose level. RESULTS Dose escalation of paclitaxel continued to 225 mg/m2 without dose-limiting toxicity, but further escalation was not attempted because of the known likelihood of neuro-toxicity above this level. Instead, ifosfamide was increased to 4 g/m2 for the final level. At these doses, dose-limiting myelosuppression was not seen, and there was only 1 episode of febrile neutropenia in 164 treatment cycles. Drug-related toxicities of ifosfamide included gross hematuria and confusion in 1 patient each, and paclitaxel-related symptoms included flu-like syndrome in most patients, mild to moderate arthralgia and/or myalgia in 8 and 25 patients, respectively, parasthesiae in 15 patients and mild to moderate hypersensitivity reactions in 15 patients each. Partial response was seen in 20.5% of patients (CI 9.3%-36.5%). CONCLUSIONS Out-patient paclitaxel given over 3 hours and single-dose ifosfamide over 1 hour may be combined safely without the need for hematopoietic growth factors for the treatment of patients with non-small-cell lung cancer. The recommended doses for phase II study are paclitaxel, 225 mg/m2 and ifosfamide, 4 g/m2 every 3 weeks.