Super paramagnetic iron oxide (SPIO) is taken up in the bone marrow and lymph nodes, as well as by the liver. Focusing on the intervertebral disks, which are unaffected by contrast effects, we examined the relationship between magnetic resonance image (MRI) signal intensity after SPIO uptake in the vertebral body and intervertebral disks and investigated MRI signal intensity in bone marrow metastases and osteomyelitic (inflammatory) lesions after SPIO uptake by bone marrow. The lumbar spine was imaged in 5 healthy volunteers (age range, 26-48 years). A specified amount of SPIO was administered intravenously, and signal intensities before and after administration were measured. The signal intensity ratio with respect to the value before administration was calculated, and quantitative signal analysis was conducted. A similar investigation was performed in patients with bone metastasis and osteomyelitis. As a result of the metastasis, the signal intensity ratio showed a low value in comparison with normal marrow, and the osteomyelitis showed a high value in comparison with normal marrow. We report the usefulness of evaluations of changes in marrow signal intensity using SPIO in MRI.