An attempt to modify the absorption of oral Zn65 in rats was made by the addition of natural zinc acetate to the diet of male Sprague-Dawley rats. After the rats were maintained on a zinc-supplemented diet for 4 weeks, an oral dose of Zn65Cl was administered to the rats. The retention of Zn65 was determined by whole-body assay techniques. Differences in per cent Zn65 retained were attributed to differences in the zinc acetate level in the diet. Data from 1 human subject suggest that intestinal absorption may be decreased by increasing dietary zinc levels.