观察了２３例原用甲状腺片替代治疗的先天性甲状腺功能低下症（先天性甲低）患儿，改用国产左旋甲状腺素钠（Ｌ－Ｔ４）治疗前后的血清甲状腺激素水平的变化。服Ｌ－Ｔ４前１６例Ｔ３、ＦＴ３高于正常值；９例Ｔ４在正常低限；ＦＴ４除１例低于正常，均在正常范围，但其中７例为正常低值。采用Ｌ－Ｔ４后均恢复正常，有显著性差异（Ｐ＜０．０１），ＴＳＨ无明显差异。４例原为骨龄发育提前者，服Ｌ－Ｔ４两年后骨龄正常。提示Ｌ－Ｔ４为治疗先天性甲低的最佳药物。 The changes of serum thyroid hormones in 23 cases of congenital hypothyroidism (congenital hypothyroidism) treated with thyroid replacement therapy were observed before and after L-T4 treatment. T3 and FT3 in the first 16 cases of L-T4 were higher than the normal value; in the 9 cases, T4 was in the lower limit of normal; FT4 except 1 case was lower than the normal range, but 7 cases were normal low value. After L-T4 were returned to normal, there was a significant difference (P <0.01), TSH no significant difference. 4 cases were originally advanced age of bone development, service L-T4 two years after normal bone age. Tip L-T4 is the best treatment for congenital hypothyroidism.