Abstract. Cytosolic 3, 5, 3'-triiodo-L-thyronine (T3)-binding protein (CTBP) plays an important role in the regulation of intracellular T3 translocation from cytoplasm to the nuclear T3 receptor. We examined whether the CTBP activity could be induced by T3 or not in cultured hepatocytes prepared from thyroidectomized rats. CTBP activity was not detected in primary cultured hepatocytes from thyroidectomized rats. However, the protein was induced by the addition of T3 to the culture medium. The increase in the activity of CTBP was time dependent and the maximal level was obtained by 48 h in the presence of 300 nM T3. CTBP activity was also increased by retinol (35 µM) or by 1,25-(OH)2-vitamin D3 (10 nM). On the other hand, the activity of malic enzyme (ME) was induced by the addition of T3 to the culture medium. The maximal activity of ME was obtained by 48 h in the presence of 300 nM T3. The increase in ME activity was also induced by retinol or 1,25-(OH)2-vitamin D3. These results suggested that not only ME activity but also CTBP activity is induced by T3. Further, retinol and vitamin D3 have similar effects on the induction of CTBP activity and ME activity. Previously we observed that the level of CTBP was decreased by thyroidectomy in rat kidney. The level was restored by the administration of T4 without changes in the affinity constant for T3 binding [7]. These results indicated that CTBP is one of the thyroid hormone responsive proteins.Malic enzyme which is known to be induced by thyroid hormone plays an important role in NADPH production in cytosol. In this study, we examined whether the CTBP and malic enzyme could be induced by T3 or not in cultured hepatocytes prepared from thyroidectomized rat. Further we examined the effect of retinol (Vitamin A) and 1,25-(OH)2-dihydroxycholecalciferol (1,25-(OH)2-D3) on CTBP.