The nutritive utilization of magnesium and calcium was studied using two different formulations of Mg: MgCO3 and an organic dietary Mg preparation. The influence of supplementation with the latter was also studied. The dietary organic magnesium did not modify food intake, which remained adequate in all animals used in the present experiments. Magnesium in both inorganic compound and organic preparation form was well absorbed; furthermore, absorption levels of the latter remained quite stable throughout the different experimental periods. Mg balance in both muscle and femur was similar in all groups studied. Digestive utilization of Ca and Ca content in the longissimus dorsi were higher in animals fed the organic Mg preparation while Ca levels in blood and femur were not affected.