Swine fed rations containing 16, 21, 26, 31, 36, 41, or 46 parts per million of zinc gained 0.06, 0.13, 0.25, 0.52, 0.61, 0.69, and 0.76 lb, respectively, per day. Feed required per unit of gain decreased with each increment of zinc. Parakeratosis occurred in pigs fed 16, 21, 26, 31, or 36 ppm of zinc.