The proposed study is concerned with the effect of zinc on the intestinal absorption of calcium in man. The study is based on a recent observation made in this Research Unit that a high zinc intake of 140 mg supplemental zinc decreases the intestinal absorption of calcium during a low calcium intake of 200 mg/day, but not during a normal calcium intake of 800 mg/day. In the proposed study, the effect of the 140 mg dose of zinc on the absorption of calcium will be tested during a calcium intake lower than 800 mg, namely during a calcium intake of 500 mg/day. Doses of zinc lower than 140 mg, namely 100 mg and 50 mg will be tested during both a low calcium intake of 200 mg/day and during the 500 mg calcium intake. These doses of zinc and these amounts of calcium will be used in order to delineate the specific dose of zinc and the specific calcium intake at which supplemental zinc inhibits the intestinal absorption of calcium. Since previous studies have shown that the 140 mg dose of zinc does not affect the intestinal absorption of calcium at the 800 mg calcium intake it can be assumed that doses of zinc lower than 140 mg would also not have any effect and these doses will therefore not be tested. The fact that it has already been shown that zinc decreases the intestinal absorption of calcium during a low calcium intake is of relevance in terms of the calcium status of persons who take zinc supplements.