Tissues from female Fisher rats fed varying levels of magnesium (100 ppm or 700 ppm) and pyridoxine hydrochloride (PN.HCl) (7, 35, or 1500 mg/kg diet for six weeks) were dry ashed and analyzed for magnesium using atomic absorption spectroscopy. In tissues from rats consuming magnesium diets, tissue magnesium levels increased as levels of dietary PN.HCl increased. Increases in plasma, liver, kidney, and brain magnesium levels were statistically significant (p less than 0.05). With the exception of liver, no statistically significant changes in tissue magnesium levels occurred with PN.HCl supplementation in rats fed diets with adequate magnesium. Dietary supplementation with PN.HCl produces alterations in tissue magnesium levels in the rat and these alterations are modulated by dietary magnesium and PN.HCl supplementation.