Gallium nitrate is the anhydrate salt of the naturally occurring heavy metal. It has demonstrated antitumor activity in a variety of murine tumor models, including Walker carcinosarcoma 256, fibrosarcoma M-89, leukemia K-1964, adenocarcinoma 755, mammary carcinoma YMC, reticulum cell sarcoma A-RCS, lymphoma P1798, and osteosarcoma 124F. Preclinical studies performed in rats, rabbits, dogs, and monkeys showed the dose-limiting toxicity to be renal. The hepatic, pulmonary, gastrointestinal, hematologic, and integumentary systems were also involved. The major route of elimination is the kidneys, with 35%-71% of the infused dose excreted within 24 hours. Three phase I studies suggested the following phase II doses: 700-750 mg/m2 by short infusion, once every 2-3 weeks; 300 mg/m2/day by short infusion for 3 consecutive days, to be repeated every 2 weeks; and 300 mg/m2/day by continuous infusion for 7 consecutive days, to be repeated every 3-5 weeks. The major organ toxicity reported was renal; however, this can be adequately controlled either by hydration and osmotic diuresis or by use of continuous schedule. (Either maneuver appears to allow delivery of the recommended phase II dose with a less than 30% risk of change in serum creatinine.) In limited phase II evaluation, the drug has shown antitumor activity in patients with either refractory lymphomas or small cell lung carcinoma, with total objective response rates of 28% and 11%, respectively. In addition, it has been effective in the treatment of patients with cancer-related hypercalcemia by having an inhibitory effect on calcium reabsorption from bone. Single-agent phase II studies are planned in all major tumor types. Some are already ongoing in patients with genitourinary malignancies (renal, bladder, prostate, testicular), small cell lung carcinoma, and multiple myeloma. Metabolic studies are in progress at Memorial Sloan-Kettering Cancer Center to further elucidate the mechanism or mechanisms of the hypocalcemic effects.