To acquire additional data on the biodistribution of Dand DM-USPIO, we examined tissues from the liver, spleen, lung, kidney, and heart of rabbits which had undergone in vivo MRI study and had received dose 3 of either D-or DM-USPIO (n = 3, respectively); two rabbits treated with neither D-nor DM-USPIO were the controls. These specimens were fixed in 10% paraformaldehyde. Paraffin-embedded 4-µm-thick sections were cut in the axial plane and stained with Prussian blue. We assessed one section for each organ. Prussian blue-stained areas were measured and evaluated as described above.