Turnover of thiamine in various organs was investigated by giving TPD-³⁵S (inner) or thiamine-³⁵S by mouth or by subcutaneous injection to white rats and the following results were obtained:
1. The turnover ratio of thiamine in the organs was increased day by day after daily oral administration or subcutaneous injection of TPD-³⁵S (inner) or thiamine-³⁵S.
2. The turnover ratio of thiamine in the organs was distinctly higher after administration of TPD-³⁵S (inner) by either route than in the case of thiamine-³⁵S.
3. No marked difference in the turnover ratio due to difference in the route of administration, oral or subcutaneous, of both TPD and thiamine was noted.