DNA polymorphisms that can be detected by restriction endonucleases are valuable in population and linkage studies. In this manuscript we have reported on the occurrence of DNA polymorphisms in a defined region of the bovine thyroglobulin gene. We have shown that an intron 9 PstI site and an exon 11TaqI site are highly polymorphic, and occur only as the (+ +) or (–) haplotypes at a frequency of 0.53 and 0.47 respectively in Afrikander cattle. The same sites have also been found to be polymorphic in the Belgian White-and-Blue breed. An additional TaqI polymorphism in the Belgian White-and-Blue breed is also described. The role of selective pressure on the polymorphic sites is discussed.