Proopiomelanocortin (POMC) plays an essential role in the stress response of the hypothalamic-pituitary-adrenal axis, and is the precursor of biologically active peptides such as adrenocorticotropin (ACTH), $alpha$-melanocyte-stimulating hormone ($alpha$-MSH), $eta$-melanocyte-stimulation hormone ($eta$-MSH) and $eta$-endorphin. We have synthesized two different forms of POMC cDNA clones, POMC-I and POMC-II, from a pituitary cDNA library for Paralichthys olivaceus, or Japanese flounder. jfPOMC-I cDNA consists of 954bp and encodes a polypeptide of 216 amino acid residues, whereas jfPOMC-II consists of 971bp which encode a polypeptide of 194 amino acid residues. The high levels of jfPOMC-I and -II mRNAs detected in the pituitary tissue and moderate levels detected in the brain tissue plus our quantitative RT-PCR analysis, which showed there to be no significant difference between the levels of jfPOMC-I and -II mRNAs, indicate that there may be no functional separation between these two mRNAs in the flounder.