Most discussions of iron therapy include a statement about the ineffectiveness of iron ingested simultaneously with antacids. This study was designed to determine whether or not antacids inhibit iron absorption. A small-dose iron tolerance test was used to compare absorption of iron with and without various antacids. Liquid antacid containing aluminum hydroxide and magnesium hydroxide did not significantly decrease iron absorption. Sodium bicarbonate and calcium carbonate caused the plasma iron increase to be 50% and 67% less than the control values, respectively. However, when calcium carbonate was present in a multivitamin-plus-minerals tablet, the plasma iron change was not significantly different from control trials. Presumably the competitive binding of iron by ascorbic acid in the vitamin pill allowed uninhibited absorption of the iron. Our results suggest that certain antacids may be combined with iron therapy without reducing the efficacy of the iron.