Phase I clinical trial of a new semi-synthetic morpholino anthracycline derivative, KRN8602, was performed. Sixteen patients with advanced malignant neoplasms refractory to standard chemotherapies received 27 courses at doses ranging from 1.5 mg/m2/day to 18 mg/m2/day by bolus injection for three consecutive days. The dose limiting toxicity was leukopenia, and a maximally tolerated dose was 18 mg/m2/day (day 1-3). The recommended dose and schedule for a phase II study is determined to be 12 mg/m2/day for three consecutive days at 3-4 weeks intervals. Among non-hematologic toxicities, nausea and vomiting were severe, but stomatitis and alopecia were rarely observed. Clinical signs of cardiotoxicity were not seen.