Ventricular natriuretic peptide (VNP), a newly discovered type of cardiac natriuretic peptide identified in eels, has a unique amino acid sequence and biological activity compared with other members of the natriuretic peptide family. We have cloned a cDNA encoding the eel VNP precursor from a cDNA library of eel ventricles and determined its sequence. Sequence analysis showed that the preproVNP consists of 150 amino acid residues containing a signal sequence of 22 amino acid residues at its N terminus and mature VNP(1–36) at its C terminus. Comparison with two types of mammalian cardiac natriuretic peptides (A and B type natriuretic peptides; ANP and BNP) revealed that VNP showed greater overall sequence identity to ANP than to BNP at both the cDNA and amino acid sequence levels. Since VNP cDNA lacks the repetitive ATTTA sequence in the 3′ non-coding region, which is a characteristic common to all BNP cDNAs sequenced to date, VNP may differ from BNP. While mRNA for eel ANP was detected only in the atrium, that for eel VNP was more abundant in the ventricle than in the atrium. Thus VNP is regarded as the first truly ventricular hormone in terms of synthesis and storage. Southern blot analysis indicated that VNP is also present in the quail, which belongs to a taxon where BNP has already been identified.