A group of 74 patients with advanced breast cancer received elliptinium as second- or third-line treatment (100 mg/m2/week). The objective response rate was 19% (30% in soft tissue metastases), lasting from 3 to 12 months. This drug appears to have no marrow toxicity. Mild to moderate nausea and mouth dryness were the most frequently encountered side effects. Hemolysis occurred in five patients who had an IgM antibody and represents the dose-limiting toxicity. Cumulative renal toxicity (World Health Organization, grade 2) was observed in one of ten patients who had received greater than 2000 mg of elliptinium.