4'-Epi-doxorubicin is a new anthracycline analog with reduced cardiac toxicity in animal studies. A phase-II study was performed in 17 patients predominantly with non-small-cell lung cancer. All suffered from recurrent or advanced tumors and 7 of 16 evaluable patients had been pretreated with an alternative chemotherapy. 4'-Epi-doxorubicin was applied at a dose of 75 mg/m2 every 3-4 weeks. The median total dose was 280 mg (range: 130-250 mg). Only one patient with epidermoid lung cancer (overall response rate: 6%) showed a minor response and stable disease was observed in six other patients with bronchogenic carcinoma. Myelosuppression was rare and moderate: leukocytopenia of less than 2,000/mm3 occurred in 25% of patients and thrombocytopenia of less than 100,000/mm3 in 8% of patients. The frequency of alopecia and gastrointestinal side effects was 88% and 80%, respectively. Persistent electrocardiographic alterations were recorded in 2 of 14 (14%) patients. One of four patients revealed a marked reduction of left ventricular ejection fraction in radionuclide cardiography. It is concluded that 4'-epi-doxorubicin is not superior to adriamycin in this low-prospect treatment area, but studies with increased doses appear necessary in adriamycin-sensitive tumors because of recent reports from phase-III trials showing reduced cardiac and gastrointestinal toxicity with 4'-epi-doxorubicin in comparison with adriamycin.