The gene encoding the Sox F-group transcription factor Xsox17alpha(1) is specifically expressed throughout the entire region of the Xenopus blastula fated to become endoderm, and is important in controlling endodermal development. Xsox17alpha(1) is a direct target of the maternal endodermal determinant VegT and of Sox17 itself. We have analysed the promoter of the Xenopus laevis Xsox17alpha(1) gene by transgenesis, and have identified two important control elements which reside about 9 kb upstream at the start of transcription. These elements individually drive transgenic endodermal expression in the blastula and gastrula. One contains functional, cooperating VegT and Sox-binding consensus sites. The Sox sites in this region are occupied in vivo. The other responds to TGF-beta signals like Activin or Nodals that act through Smad2/3. We propose that these two regions co-operate in regulating the early endodermal expression of the Xsox17alpha(1) gene.