The cDNAs encoding two different anionic forms of Atlantic cod trypsinogen have been isolated and sequenced. The nucleotide sequences include the 5'-noncoding and 3'-noncoding regions in addition to preproenzymes of 241 amino acids. These consist of hydrophobic signal peptides, activation hexapeptides and trypsins of 222 amino acid residues. The cod trypsins contain all the major structural features common to trypsins such as the catalytic triad His57, Asp102 and Ser195. Furthermore, the obligatory Asp189 and the six disulphide bonds are conserved. Eight amino acid residues are different between the isozymes, leading to a difference of four charges. Both cod trypsins are one-amino-acid-residue shorter than most mammalian trypsins as a result of deletion of proline at position 152, and have a high methionine content. In addition, the cod preproenzyme signal and activation peptides differ markedly from their mammalian analogues. The amino acid identity between the cod and bovine trypsins is approximately 60%.