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A new participate magnetic resonance (MR) contrast agent was prepared by controlled precipitation of iron oxide in an aqueous starch solution. The potential of the magnetic starch microspheres (MSM) as a hepatosplenic contrast enhancer was studied by MR spectroscopy and MR imaging. Intravascular administration of MSM to rodents showed an effective blood clearance and a tissue-specific localization of the substance. MSM doses in a range of 0.3–1.5 mg Fe/kg caused a 50% alteration in sensitive contrast parameters (ED50 doses) of liver and spleen. The contrast effect of MSM in liver and spleen was halved within 2 to 5 days. The approximated lethal MSM dose in mice was 150–200 mg Fe/kg. MSM is a tissue-specific MR contrast substance with high efficacy, rapid bioelimination, and low acute toxicity.