True calcium absorption was studied as a function of the size of the ingested load in healthy adult women, under meal conditions and at loads ranging from 15 to 500 mg calcium. Fractional absorption was highly inversely correlated with the logarithm of load (P less than 0.001). At the lowest loads, absorption averaged 64.0% and at the highest, 28.6%. The parameters of the best-fit relationship permit reasonably precise calculation of the impact of various calcium dosing and dietary strategies.