A phase I study of 4'-epi-Adriamycin (4'-epi-ADM) was performed in 22 patients with various types of advanced solid tumors. Very preliminary results would indicate that the drug produces a pattern of acute toxicity which is similar to that of Adriamycin. However, the incidence of vomiting, alopecia, and marrow suppression was less pronounced than that of Adriamycin. 4'-Epi-ADM prolonged the systolic time interval, although no patient presented clinical signs of cardiotoxicity. Two patients with renal carcinoma and malignant melanoma showed objective improvement. Present results suggest that further clinical studies with 4'-epi-ADM are indicated.