Two cases of congenital hypothyroidism with goiter are reported. The first was that of a 15-yr-old girl with typical goitrous cretinism, the second of a 12-yr-old boy with congenital goitrous hypothyroidism of a milder degree. Extensive clinical and biochemical studies revealed a complete absence of thyroglobulin. The only thyroidal iodoprotein detected, whether by stable or radioactive iodine analysis, had the characteristics of iodinated serum albumin. This iodoprotein was also detected after in vivo125I labeling in the serum of one case in which it was sought. Non-iodinated thyroglobulin immunoreactive material of small molecular weight was present in very small concentrations in both glands, representing probably normal or abnormal precursors of thyroglobulin. Other inherited biochemical defects in hormonogenesis could not be detected in these cases. It is concluded that absence of thyroglobulin synthesis may represent one of the causes of congenital hypothyroidism with goiter (thyroid dyshormonogenesis). In such cases, hormonogenesis is apparently supported by thyroidal iodination of serum albumin. Further studies of similar cases are needed for a better elucidation of this disorder.