We have determined the expression patterns of the met proto-oncogene and the gene which encodes its ligand, scatter factor/hepatocyte growth factor (HGF-SF), during mouse embryogenesis. A recurring pattern of expression was found in a variety of different organs: expression of met in specific epithelial cells, and transcripts for the HGF-SF gene in mesenchymal cells in close vicinity. Exchange of signals between mesenchymal and epithelial cell compartments are important in morphogenesis and differentiation of a variety of embryonal organs, although their molecular basis has not been elucidated. The observed expression of met and HGF-SF during development suggests that this receptor and its specific ligand might play a role in such processes. In addition to this distinct pattern, expression of met in certain epithelia and HGF-SF in the surrounding mesenchyme, we find met transcripts in neural, endothelial and muscle cells and transcripts for HGF-SF in neural and muscle tissue. In no instance did we observe both, transcripts for the receptor and the ligand, in the same cells. This suggests a paracrine mode of action for HGF-SF and its receptor during development. This exchange of signals might thus regulate a variety of processes, notably among them mesenchymal epithelial interactions.