1. The baseline blood thiamin concentration increased gradually during the long-term administration of TTFD, and the blood concentration was dose-dependent. The cumulative urinary thiamin excretion showed the same dose-dependence as the blood concentration. 2. The baseline blood riboflavin concentration also increased steadily during the administration period, but the increase was less than that of thiamin. Dose-dependence of the cumulative urinary excretion of riboflavin was noted. 3. No side effect were observed.