The Wingless (Wg)/Wnt signaling pathway activates High Mobility Group (HMG)-box transcription factors of the T-cell Factor (Tcf)/Lymphoid Enhancer Factor (LEF) subfamily and mediates diverse functions in development, possibly including endoderm and gut differentiation. Determinants of tissue specificity in the response to Wg/Wnt signaling remain unknown. We have identified Tcf-4 as the predominant Tcf/LEF factor in the developing mouse gut. During fetal development, Tcf-4 mRNA expression is restricted to gut epithelium and specific regions of the brain, the thalamus and roof of the midbrain. In adults, expression is widespread, with highest levels observed in the liver, an endodermally derived organ, and persists in the gastrointestinal tract. Murine Tcf-4 has multiple RNA splice variants with consequently significant heterogeneity in sequences 3' to the HMG box. Microinjection of mRNA or plasmid DNA encoding Tcf-4 into Xenopus embryos results in ectopic expression of molecular markers of endoderm and differentiated gut epithelium in isolated animal cap explants. Taken together, these findings point to a potentially important function for Tcf-4 in development of the vertebrate gastrointestinal tract.