Ca-supplemented diets (containing 1.0% Ca) were prepared by substituting milk, cheese, yogurt, CaCO3, or Ca citrate-malate (CaCM) into 2 control diets (containing 0.5% Ca and either no lactose or 20% lactose). The diets were labeled with 59Fe and offered to fasted rats aged 21 d, 40 d, and 100 d. Fe absorption was determined by whole-body counting. The effect of Ca supplementation was most pronounced in the 21 d rats where supplementation with yogurt, CaCM, and CaCO3, but not milk or cheese, depressed 59Fe absorption (p<0.05). In 40 d rats, supplementation with CaCM but none of the other sources depressed 59Fe absorption. There was no effect with any of the sources in the 100 d rats. Lactose dramatically increased 59Fe absorption from the milk and control diets in 21 d rats, decreased 59Fe absorption from CaCM in 40 d rats but had no effect in other treatments. These data suggest that Ca in the form of CaCO3 and CaCM, has a more pronounced effect on iron bioavailability than Ca in dairy products (except for yogurt) and that Fe−Ca interactions are influenced by the physiological state of the animal.