An enriched soy, in which 75mg of thiamine, 75mg of riboflavin and 750mg of niacinamide were added per 2 litres, was introduced into a farm-village where ariboflavinosis was found endemically among the inhabitants. Observations on its effect were made from February to October 1956. By the use of the enriched soy, it was supposed that the daily intake of riboflavin was increased from 0.4mg to 1.0mg. Both ariboflavinotic signs and urinary outout of riboflavin were monthly examined on 10 boys with use of the enriched soy and on 20 boys of the control, and the blood riboflavin level was estimated on October 1956. As a consequence of the use of the enriched soy, an improvent of ariboflavinotic signs, an increase in the urinary output of riboflavin and an increase in the esterified vitamin in blood were observed.