Biodegradable implants continue to be of interest in orthopaedics for their many potential applications. The magnesium (Mg) alloy WE43 is a biodegradable material with the CE mark approval for clinical application and today mostly used as screws for dental prosthesis. Additional to magnesium, WE43 contains rare earth elements (REEs) of around 7 wt%. These REEs are needed to give the material its mechanical properties and corrosion resistance. Although WE43 is a promising material thought to be used in a diverse number of orthopaedical applications, questions have risen regarding the potential long-term effects of these REEs on the body after the implant degrades. Additionally, with the global demand of REEs rising and a decreasing supply of these elements, there may also be a potential future problem regarding the availability of materials based on REEs. Therefore, new materials containing only elements naturally found in the body are of interest. One such material is the novel Mg-Ca alloy, X0. In this study, a biological comparison was made to answer the question whether the biological performance of X0 is comparable to the already CE approved WE43. Viability, proliferation, and differentiation of MC3T3-E1 (preosteoblast) cells combined with extracts from X0 and WE43, respectively were used. An additional experiment was conducted were X0 was tested against three different versions of WE43 and titanium. In summary, the X0 alloy performed similarly to WE43 in all testing. Both WE43 and X0 showed indications of being bioactive. This led to the conclusion that the X0 alloy showed promise for future use and being a viable alternative to WE43.