The bioavailability as calcium sources of dibasic calcium phosphate, calcium lactate and calcium carbonate was compared by means of in vivo and in situ experiments. For the in vivo experiment, vitamin D-deficient rats were fed ad libitum on food containing either dibasic calcium phosphate, calcium lactate or calcium carbonate with oral administration of vitamin D₃ (200IU/rat/day). There were no significant differences in body weight, food consumption or plasma concentrations of calcium, phosphorus and 25-hydroxyvitamin D₃ among the three groups after one week. In the in situ experiment, intestinal calcium absorption of the three calcium compounds was studied using an intestinal loop circulation method using vitamin D-replete and vitamin D-deficient rats. Again, little difference was observed among the respective data for the three calcium compounds. From these results, we concluded that there was practically no significant difference among the three compounds with regard to their bioavailability as calcium sources.