Magnetic resonance imaging (MRI) of normal fracture repair was evaluated in six randomly chosen adult patients with solitary, closed fractures of the tibial shaft by obtaining serial MRI scans until union of the fracture. The mean time to union was 14.3 weeks. Ultralow-field 0.02-Tesla magnet equipment was used. The MRI scans showed a characteristic pattern of events common for all the patients studied and compatible with the recognized histomorphology of fracture repair. The intramedullary cavity demonstrated a marked decrease in the signal intensity. In the soft tissues surrounding the fracture the initially evenly high signal intensity gradually developed a granular appearance with embedded low-intensity nodules. These nodules corresponded to the first areas to become mineralized, as could be seen on plain radiographs several weeks later. The question of whether MRI renders it possible to predict delayed union calls for continued investigations.