Magnetic iron oxide nanoparticles have intrinsic advantages over other nanoparticles for various biomedical applications. These advantages include visualization, heating, and movement properties. There are now numerous efforts underway to expand the applications of these particles for non-invasive magnetic targeting/localization, drug/adjuvant delivery and release, cellular imaging and cellular therapies. In order to move these applications forward it is necessary to define new assays and methods to visualize, move and heat these particles and define their interactions with cellular systems. Our studies of the movement and heating of these nanoparticles in solutions and gels suggest a strong response of these properties to the size and coating of the particles, the suspending medium and the field parameters. Additionally, cellular association is a strong function of the coating and concentration of the nanoparticles and the time of incubation. X-ray computed tomography (CT) can be used to image at least two orders of concentration (1-40 mg Fe/ml) higher than that by 1.5 T Magnetic Resonance (MR) (0.01-0.4 mg Fe/ml) and could prove to be useful for image-guided treatments in vivo.