Two c-myc genes have been isolated from a tetraploid fish, the common carp (Cyprinus carpio). The nucleotide (nt) sequences of the two genes and their flanking regions (CAM1, 8675 bp and CAM2, 5784 bp) have been determined. Both genes contain two coding exons which are homologs of c-myc exons 2 and 3 in higher vertebrates. The nt sequence homologous to c-myc exon 1 of higher vertebrates has not been found. Carp CAM1 and CAM2 presumably encode peptides of 394 and 401 amino acids (aa), respectively. These two peptides share 55-91% aa identity with those of humans, chickens, frog, rainbow trout and zebra fish. The two carp c-Myc have a Glu stretch at the beginning region of exon 3. This Glu stretch is also present in zebra fish, suggesting that it may be characteristic to c-myc genes of cyprinid fishes. The existence of two c-myc in carp is attributed to the tetraploid nature of carp. These two genes share 92.4% nt identity in the coding region and 84.2% in the intron. The two deduced peptides share 94.2% aa identity, suggesting that the tetraploid event probably occurred 58 million years ago. Both of the genes' cDNA clones were obtained from a cDNA library of carp peripheral blood leukocytes, implying that both of the genes are expressed.