Mitonafide is the lead compound of a new series of antitumor drugs, the 3-Nitronaphthalimides, which have shown antineoplastic activity in vitro as well as in vivo. This phase I Mitonafide study in non-small cell lung cancer using a 120-hour continuous infusion (120 h. C.I.) schedule of administration was designed to deliver the maximum amount of drug while avoiding the risk of central nervous system (CNS) toxicity, previously observed in studies with daily short (1 hour) administration schedules. Twenty patients were treated at doses ranging from 107-200 mg/m2 x 120 h. C.I. Dose-limiting toxicity with this schedule of administration was leukopenia. Other toxicities were mild or not relevant. No CNS toxicity was observed. The recommended dose for phase II C.I. Mitonafide studies is 170 mg/m2 x 120 h. C.I. in previously untreated patients. Plasma level monitoring is recommended.