A clinical study was designed to evaluate the tolerance of cancer patients to liposome-associated doxorubicin (L-DXR). The liposomes used contain phosphatidylglycerol, phosphatidylcholine, cholesterol, and DXR intercalated in the lipid bilayer, and have a mean size in the range of 0.3-0.5 μm. Thirty-two patients, most of them with primary or metastatic liver cancer refractory to conventional therapy, were entered into the study. A total of 69 courses of therapy was administered by intravenous infusion of a suspension of L-DXR (0.5-2.0 mg DXR/ml) in physiologic saline at an approximate rate of 2 ml/min given on a 3-week intermittent schedule. The L-DXR and phospholipid doses were escalated from 20 mg/m2 and 0.3 g/m2 to 120 mg/m2 and 3.2 g/m2 respectively. Treatment was generally well tolerated and acute toxic effects such as nausea and vomiting were mild and infrequent. Chills and fever (>38.0°C) were observed in three patients during infusion of L-DXR and in seven patients 6-12 h after the end of infusion. Median WBC nadir counts were 2700, 2300 and 700/μl at 85, 100 and 120 mg/m2 respectively. All three patients receiving 120 mg/m2 developed grade 4 leukopenia and fever requiring intravenous antibiotics, and, in two of them, severe stomatitis (grades 3 and 4) was observed. Significant hair loss was apparent in all patients receiving doses higher than 50 mg/m2. The maximal tolerated dose of L-DXR appears to be 120 mg/m2, with leukopenia and stomatitis being the dose-limiting factors. While the subacute toxicity of L-DXR appears to be qualitatively similar to that of free DXR, its tolerance exceeds the recommended dose of free DXR (75 mg/m2) in the standard 3-weekly schedule.