It was observed by human experiment that the folic acid excreted in feces as well as the vitamin synthesized markedly increased with the change of an ordinary diet to a vegetable one. On the contrary, both values of the vitamin decreased after the diet was switched from an ordinary diet to a meat one. The addition of cellulose to each diet caused a definite rise in both amounts of the vitamin, suggesting that the main promoting effect of the vegetable diet is due to cellulose contained therein. The rise in the vitamin is roughly proportional to the increase in the amount of feces. The vitamin in urine was very low in amount as compared with that in feces.