The mouse Fgf-1 gene contains at least four upstream promoters that are alternatively spliced to the first protein coding exon, giving rise to different Fgf-1 mRNA variants (1.A, 1.B, 1.C, and 1.G), each expressed in a tissue specific manner. Only the Fgf-1.A promoter contains TATA and CAAT consensus sequences, and its corresponding mRNA is mainly expressed in the mouse heart. In situ hybridization with an Fgf-1.A-specific cRNA probe showed the 1.A message to be very low in embryonic heart, tongue, spinal cord and smooth muscle of the small intestine. Moderate 1.A mRNA levels were revealed in head mesenchyme, paraxial mesoderm, in the embryonic inferior cunniculus, hyppocampus, and thymus. These results suggest a limited role of the Fgf-1.A mRNA variant during development.