2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been shown to induce cleft palate, in which the molecular etiology of the defect is poorly characterized. Recently, transforming growth factor-beta3 (TGF-beta3) has been indicated to play an essential role in the development of palatal shelves. In this developmental toxicity study, we investigated the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the expression of TGF-beta3 in fetal mice. Pregnant C57BL/6 mice were exposed to corn oil or TCDD (32 microg/kg/day 64 microg/kg/day, per os) at embryonic day 10 (ED10), a drastic inhibition of palatal shelves was induced. By using RT-PCR (reverse transcription-polymerase chain reaction) and Western blot, the expressions of TGF-beta3 was investigated. We found that the expression of TGF-beta3 was gradually up-regulated in TCDD-treated group. These results suggest that cleft palate can be induced by TCDD exposure, the modification of TGF-beta3 is related to its pathogenesis.