Salamanders are often used as representatives of the basal tetrapod body plan in functional studies. However, little is known about the loads experienced by their limb bones during locomotion; previous studies of bone loading have focused mainly on animals such as mammals and birds with parasagittal limb posture. This study evaluates the loads on the limb bones of the tiger salamander (Ambystoma tigrinum) during ter- restrial locomotion using three-dimensional measurements of the ground reaction force (GRF) and hindlimb kinematics, as well as anatomical measurements of the femur and hindlimb muscles. Peak GRFs acting on a single limb were about half the body weight of the salamander. The GRF is initially oriented posteriorly but shifts to an anterior direction later in the step, and has very little medio-lateral inclination. At the time of peak stress, the GRF is primarily vertical and perpendicular to the fe- mur. Peak stresses were generally below 15 MPa, which is fairly low compared to observations from other vertebrate lineages. The peak stress was primarily associated with dorso-ventral bending, which may be par- tially due to a lack of activity in knee extensor muscles that span the length of the femur. Comparisons of stress magnitudes to mechanical property data for salamanders indicate their limb bones may have safety factors as high as 10 or more. Together with data from other amphibian and reptile lineages, these results suggest that low magnitude loading and high limb bone safety factors may have an ancient evolutionary his- tory. Supported by NSF (IOB-0517340).