The pentose cycle of the thiamine-deficient rats was studied by tracing the isotope activity in the liver slices, when they were incubated with ^<14>C-glucose. 1) ^<14>CO_2 production was decreased with U-^<14>C-glucose. 2) More ^<14>CO_2 was seen with 1^<14>C-glucose than 6^<14>C-glucose. 3) U-^<14>C-glucose incorporation into RNA-fraction was decreased which was restored by the addition of TDP or TTFD. 4) Transketolase activity was low. The contents of fat or protein in the diets did not influence the incorporation into RNA and transketolase activity. These results suggested that nucleic acid metabolism via transketolase plays a role in thiamine-deficient state.