We have examined by Northern analysis and in situ hybridisation the expression of TGF beta 1, beta 2 and beta 3 during mouse embryogenesis. TGF beta 1 is expressed predominantly in the mesodermal components of the embryo e.g. the hematopoietic cells of both fetal liver and the hemopoietic islands of the yolk sac, the mesenchymal tissues of several internal organs and in ossifying bone tissues. The strongest TGF beta 2 signals were found in early facial mesenchyme and in some endodermal and ectodermal epithelial cell layers e.g., lung and cochlea epithelia. TGF beta 3 was strongest in prevertebral tissue, in some mesothelia and in lung epithelia. All three isoforms were expressed in bone tissues but showed distinct patterns of expression both spatially and temporally. In the root sheath of the whisker follicle, TGF beta 1, beta 2 and beta 3 were expressed simultaneously. We discuss the implication of these results in regard to known regulatory elements of the TGF beta genes and their receptors.