The effect of a Mg-deficient diet (200 mg Mg/kg feed) on the bioavailability of dietary Zn and the concentration of this cation in plasma, whole blood, skeletal muscle, kidney, heart and brain of Wistar rats was studied after 7, 35, 42, 49, 56, 63 and 70 d. Mg deficiency significantly decreased Zn in whole blood on day 42 of the experiment, but there was no significant change in plasma Zn throughout the 70 d study period. The Mg-deficient diet significantly increased intestinal absorption of Zn, Zn balance, and Zn concentration in femur and kidney, but decreased Zn concentration in the heart despite the increase in dry weight of this organ. No change was found in brain Zn concentration.