Twenty-four steer calves of beef breeding and averaging 235 kg. in body weight initially were group fed for 84 days in four replicated lots of three steers each to study the effects of supplemental dietary iron. Three treatments included 0, 400 and 1,600 ppm iron as ferrous sulfate added to a basal diet containing 77 ppm iron. Average daily feed intake and average daily gain were depressed by as little as 400 ppm iron. Total plasma copper was reduced (P<.05) and plasma inorganic phosphorus was increased (P<.05) by feeding 1,600 ppm supplemental iron. Dietary iron did not affect blood hemoglobin or hematocrit. Iron concentrations in the liver, spleen, kidney and heart were increased (P<.05) and copper and zinc concentrations of the liver were decreased (P<.05) by feeding high dietary iron. Dietary iron treatments did not appear to affect the magnesium or manganese content of the tissues studied. The response of animals given a variable iron treatment in which 3,200, 2,400 and 0 ppm supplemental iron were fed for consecutive 21-, 28- and 35-day periods, suggested that the effects of excessive levels of dietary iron may be quite transient.