Objective Superparamagnetic iron oxide (SPIO) particles are phagocytosed by cells of the macrophage-monocytic phagocytic system. They are usually used in MRI as a negative contrast agent, because of their strong T2* effect, to improve detection of tumors in the liver and spleen. However, they also have a potent T1 relaxivity. In the current study, we describe this T1 effect in liver hemangiomas. Materials and Methods Twelve patients (nine women and three men, aged from 38 to 76 years) with liver hemangiomas were examined by means of MRI at 1.5 T before and after intravenous administration of SPIO particles at a dose of 15 μmol Fe/kg body wt. Signal intensity was measured from regions of interest. Results Whereas on postcontrast T2-weighted SE images the hemangiomas showed on average a signal drop of 20% (p = 0.011) and 49% (p = 0.001) (first and second echo, respectively), their signal increased by 106% (p = 0.001) on postcontrast T1-weighted SE images. Conclusion The T1 effect (signal enhancement) we observed in liver hemangiomas after infusion of SPIO particles could prove to be a useful new diagnostic feature that would help characterize these common lesions and differentiate them from other liver tumors.