A congenital goiter with impaired thyroglobulin synthesis has been investigated for the presence of messenger RNA coding for thyroglobulin. Using complementary DNA to beef 33 S thyroglobulin mRNA as a probe, we have found that thyroglobulin related sequences are present in the goiter but at a concentration lower than in normal human thyroids. We conclude that the disease is not due to a complete deletion of thyroglobulin gene.