Magnesium (Mg) and its alloys are being widely investigated for their potential use as resorbable biomaterials for orthopaedic applications. However, the natural corrosion of the metals results in potentially harmful perturbations to the physiological environment, which requires a comprehensive understanding of their biocompatibility. Currently, most investigations proceed directly from in vitro biocompatibility studies to intraosseous implantation. However, this can result in the unnecessary elimination of appropriate materials due to over sensitive in vitro methods or the implantation of potentially harmful materials. This study involved the development of a relevant in vitro cell culture method, and an in vivo soft tissue implantation technique to provide an intermediate step between basic cell culture methods and large animal intraosseous investigations. A Live/Dead fluorescent assay was used to investigate the viability of both L929 and SaOS-2 cells exposed to Mg alloys, with the results compared to those seen with the intramuscular implantation of the same materials in Lewis rats. These methods were able to successfully provide data on the corrosion of Mg alloys, allowing the identification of slowly and safely corroding materials that may be used in future intraosseous investigations.