Sixty-five patients with advanced solid tumors were treated with 4'epi-doxorubicin, a new analogue of doxorubicin (DXR). Forty-three of 61 evaluable patients had not received previous chemotherapy and/or hormonal treatment. 4'Epi-doxorubicin has been administered at the dose of 75 mg/m2 i.v. once every 21 days, for a minimum of 2 courses. The pattern of acute toxicity was similar to that of DXR. Transient electrocardiographic abnormalities were found in about 50% of patients. The ratio of pre-ejection period to the left ventricular ejection time (PEP/LVET) increased within 1 h after drug injection and returned to near basal values after 24 h. Three patients received a total dose of more than 550 mg/m2, still maintaining a baseline PEP/LVET ratio near to pretreatment values. Up to now, no patient has developed clinical signs of heart failure. Partial responses were seen in patients with tumors generally sensitive to DXR such as breast carcinoma (6 of 14) and soft tissue sarcomas (2 of 6), and in patients with tumors generally resistant to DXR such as melanoma (1 of 9), colorectal carcinoma (3 of 18) and pancreatic carcinoma (1 of 2). These data suggest that 4'epi-doxorubicin may have a broader spectrum of antitumor activity than DXR.