Hyporetinemia is observed in several pathological conditions including a primary deficiency of vitamin A and has also been reported to accompany inflammatory diseases. Experimental magnesium (Mg) deficiency in rodents is accompanied by an inflammatory syndrome. The present study was designed to determine whether the acute phase response in Mg-deficient rats can modify vitamin A status. Clinical symptoms of acute phase response were observed in Mg-deficient rats and were accompanied by a reduction in plasma retinol and of plasma retinol binding protein (RBP). Mg deficiency in rats resulted in hyporetinemia without a significant decrease in liver retinol reserves. Consequently, the data strongly suggest that the decrease in plasma retinol concentration, resulting from the level of its binding protein, is related to the inflammatory effect of Mg deficiency. These results point to the possible interference of Mg deficiency on the use of plasma retinol as an indicator of vitamin A status.