Our goal was to analyze the changes in morphology and physiological function (phagocytosis, migratory capabilities, humoral and cellular response, and nitric oxide secretion) of murine macrophages after labeling with a clinically used superparamagnetic iron oxide (SPIO), ferucarbotran. In SPIO-treated macrophages, nanoparticles were taken up in the cytoplasm and accumulated in a membrane-bound organelle. Macrophage proliferation and viability were not modified after SPIO labeling. Phagocytic function decreased after labeling with only 10 µg Fe/mL SPIO, whereas other functions including migration and production of tumor necrosis factor-α and nitric oxide increased at the highest SPIO concentration (100 µg Fe/mL). Copyright © 2008 John Wiley & Sons, Ltd.