Whole sera of Mullet (Mugil so-iuy Bffsilewsky) analysed by electrophoresis acryamide discontinuous gradient gel (4 .75%+7%)showed 25-30 bands. The highest mobility fraction consists of albumin components and several preprotein components. The largest band is composed mainly of albumin components. Liporoteins with large iuolecular size axe localized at the negatiVo pole. A specific protein hand was observed in the sera of the female fish by discontinuous gradient polyacrylamide gel but was not found in the males. The specific female serum protein migrates as a protein of medium molecular site which is distinctly different from albumin arad. globulin. Thus discontinuous gradient polyacylamide gel electrophoresis affords a highly sensitive and more practical teehnique for analysis of proteins.