A phase I clinical study was done with quelamycin, a recently synthesized triferric derivative of adriamycin. Twenty-one good-risk patients were studied: 19 patients with non-small cell carcinoma of the lung and two patients with metastatic sarcoma. Acute toxicity occurred in all patients and consisted of high fever, flushing, hypertension, generalized body aches, tremors, and confusion, which lasted 3-6 hours. Potentially dangerous cardiotoxicity occurred in eight patients who had previous minor rhythm disturbances, and was characterized by tachycardia, atrial extrasystoles, atrial fibrillation, and branch block which lasted 6-14 hours. The dose-limiting hematologic toxicity was found to occur at 125 mg/m2 iv single-dose. Objective responses were observed in three of 19 patients with lung cancer and in one patient with metastatic osteogenic sarcoma resistant to adriamycin therapy. In conclusion, quelamycin is a new derivative of adriamycin with potential interest. However, the acute generalized toxicity and the immediate cardiotoxicity found in the presently used schedule are excessive. Further studies directed to suppress these side effects are in progress.