We have isolated the cDNA encoding a myogenic factor expressed in embryonic trout muscle by hybridization with a Xenopus MyoD cDNA. Nucleotide sequence analysis and amino acid comparison showed that this cDNA called TMyoD encodes a polypeptide of 276 amino acids with 70% identity to the entire Xenopus MyoD protein and 92% identity within the basic and myc-like region. Results from Northern blotting showed that the corresponding transcript is expressed both in adult and embryonic skeletal musculature and in an in vitro myogenesis system, but is undetectable in cardiac and smooth muscles and in non muscle tissues.