In order to determine the fluctuation of vitamin B(1) in the urine after drinking "Yakult", cow's milk fermented by some sort of "Family Lactbacillaceae", the authors made normal adults and patients with lung tuberculosis drink one bottle (60 cc) a day of Yakult successively, and estimated their content of vitamin B(1) in their urine polarographically and with paper chromatography. Results are as follows. 1. In the case of one bottle (60 cc) of Yakult successively, there occurs a little increment of vitamin B(1) content in their urine of normal adults comparing with tuberculous patients receiving chemotherapy. 2. In the case of taking one bottle of Yakult, no marked effect can be recognized in their urine of tuberculous patients receiving chemotherapy. However, when three bottles (180 cc) of Yakult are given every day, marked increase of vitamin B(1) can be observed even in their urine of the patients, and also impeding factor in polarographical estimation disappears, proving that Yakult is considerably effective in improving vitamin B(1) metabolism.