Human fetal kidney cells were grown in TC Med. 199 containing thiamine and its derivatives, such as TPD, TATD, BTMP, BTDS and TTFD at high concentration equivalent to 50μg per ml of thiamine hydrochloride. The effects of these compounds on the cell growth were studied. As a result, it was recognized that TPD and TATD at high concentration had remarkable inhibitory effects on the cell growth, especially in the former, however, TTFD, BTDS and BTMP had no such significant effect. On the other hand, thiamine showed no such effect on the cell growth.