The feeding of either 2 parts rock phosphate (containing approximately 3.5 per cent fluorine) or 100 grams sodium fluoride in 100 pounds of a basal ration to pigs resulted in decreased gains, increased feed requirements, and a marked decrease in the breaking strength of the femurs over lots receiving the same basal ration supplemented with either limestone, steamed bone meal, or smaller amounts of sodium fluoride or rock phosphate. It was observed that the fluorine content of the femurs was directly proportional to the amount present in the feed.