We evaluated the role of gallium nitrate infusion in the treatment of metastatic breast cancer. Gallium nitrate was administered at 300 mg/m2/day for 7 days every 3 weeks by continuous infusion concomitantly with oral calcium supplement of 500 mg twice daily and oral hydration. Fifteen patients with refractory metastatic breast cancer received such treatment for a total of 30 courses. Median age was 51, and median performance status (Zubrod scale) was 1. These patients had minimal prior chemotherapy (median 1 regimen). All patients were evaluable for toxicity and 14 for response. Nine patients had one to two metastatic sites, five patients had three to four sites. No major objective response was seen, but one patient had a minor response (10 weeks), and another showed no change in disease (16 weeks). Diverse low-grade toxicities were observed, including nausea and vomiting in 11 patients, anorexia in 11, diarrhea in eight, stomatitis in five, dysgeusia in six, musculoskeletal pain in five, skin rash in seven, partially reversible tinnitus and/or mild hearing loss in four and sensory neuropathy in two. A consistent drop in hemoglobin (median of 3.2 g/dL per patient) necessitated blood transfusion in seven patients. There was no granulocytopenia or thrombocytopenia; however, significant lymphopenia was noted. Reversible, moderate nephrotoxicity occurred in two patients. The hypocalcemic effect was consistent, with a median drop in serum calcium of 1.25 mg/dL per course. There was no hepatic toxicity. While no single toxicity was severe, overall toxicity adversely influenced treatment tolerance. Gallium nitrate by continuous infusion, as given in this study, has no activity in metastatic breast cancer.