Superparamagnetic iron oxide (ferrite) particles were evaluated as a contrast agent for magnetic resonance (MR) imaging. In this pilot study, doses ranging from 10 to 50 mumol/kg were administered intravenously to 15 patients. Ferrite-enhanced images of the liver obtained with standard pulse sequence techniques significantly increased the number of hepatic lesions detected (P less than .01) and reduced the threshold size for detection to 3 mm (P less than .01). The improved clinical performance of ferrite-enhanced images correlated with significant increases in measured contrast-to-noise ratios (P less than .01). Degradation of superparamagnetic activity and/or clearance of ferrite from the liver was demonstrated as early as 12 hours after injection, suggesting that the lack of chronic toxicity observed in animal studies may be reproduced in humans. These initial clinical results appear to confirm extensive preclinical data indicating that ferrite administered at a dose of 20 mumol/kg has the potential to significantly improve the performance of abdominal MR imaging.