We report the mapping and developmental expression pattern of the gene encoding mouse GATA-6, a member of a family of transcription factors involved in tissue-specific gene expression. Using backcross analysis, the Gata6 gene was localized to mouse chromosome 18, linked to the gene encoding transthyretin. RNase protection analysis showed that Gata6 is abundantly expressed in the heart, stomach, intestine, and ovaries of the adult mouse. The developmental expression patterns of Gata6 and the closely related gene Gata4 were directly compared using in situ hybridization. Both genes were found to be highly expressed in the myocardium, stomach epithelium, and small intestinal epithelium throughout mouse development. Of the two genes, however, only Gata6 was expressed in vascular smooth muscle. The overlapping distributions of GATA-4 and GATA-6 transcripts in the heart support the possibility of functional redundancy or interplay between these two transcription factors in this tissue. The presence of GATA-6 mRNA in vascular smooth muscle suggests that this transcription factor may play a distinctive role in gene expression in this cell type.