OBJECTIVE: To investigate the role of Pax8 in the pathogenesis of congenital hypothyrodism. METHODS: Genomic DNA was extracted from peripheral blood lymphocytes and PCR SSCP Direct DNA sequencing was applied to study exon 2～exon 9 of Pax8 gene in fifty patients who had been detected by neonatal screening or endocrinologists and diagnosed as having congenital hypothyroidism. RESULTS: No mutation was demonstrated in the encoding regions of Pax8 gene. CONCLUSIONS: Structural changes in Pax8 gene may not play an important role in pathogenesis of primary congenital hypothyroidism.