Froliferation or atrophy of lingual papilla, red or violet-red color, fissure formation and edematous appearance of the tongue, and stomatitis angularis were observed, and each of the signs was proved to be in a close relationship with riboflavin deficiency. 1) The average value of blood total riboflavin of 103 patients who showed most of the signs above mentioned, was 5.4±0.5 μg%, while it was 7.4±1.2 μg% in 46 healthy subjects. This difference is stochastically significant. 2) The average value of blood total riboflavin of each group of patients showing some single sign, irrespective of its kind, was also found to be lower than that of healthy group. 3) Reverse correlation with stochastical significance was found to exist between the number of the lingual signs and the value of blood total riboflavin. 4) Urinary excretion of riboflavin appeared to bear no direct relationship with these lingual signs.