RESUMEN
Wealing Wistar rats fed a diet with casein as the only source calcium showed less weight gain as compared to controls receiving calcium carbonate besides casein in the diet. Food intake was also diminished in that group, although the animals ingested sufficient calcium for normal growth. Apparent absorption of the mineral was twice that of the controls but this was not enough for normal mineralization, as showed by bone rarefaction in the experimental group. Bone calcium was also lower in theese animals. The data indicate that when using casein as a protein source in experiments concerning calcium bioavailability one must take into consideration that part of the requirements of the mineral will be supplied by asein itself. Key words: calcium; biovailability; casein