For weanling pigs, the practical minimum level of riboflavin appears to be approximately 1.4 mg. per pound of ration consumed in the drylot experiments herein reported. Hughes (1940) reported a minimum requirement of between 1 and 3 milligrains of riboflavin per 100 pounds body weight per day. This would be equivalent to 0.25 to 0.75 rag. per pound of ration consumed if the pig ate 4 pounds of feed per ioo pounds of body weight daily. The National Research Council Committee on Animal Nutrition (1944) recommends 3.8 milligrams of riboflavin daily per day for a 100-pound pig, or .76 milligram per pound of ration. Van Poucke and Krider (1946) reported more rapid and more efficient gains of weanling pigs fed 1.5 milligrams of riboflavin per pound of purified diet than when 0.5 or 0.75 rag. was fed.