Chromograninsandsecretograninsconstituteafamilyofuniquelyacidicproteinsthatareco-storedwithneurotransmittersandpeptidehormonesinthebrainandthediffuseneuroendocrinesystem(Winkler,H.&Fischer-Colbrie,R.1992).Structurallytheseproteinsareproductsofdifferentgenesbutsharesomeoverallpropertiessuchasanabundanceofacidicaminoacidresiduesandseveralpairsofbasicaminoacidsaspotentialpositionsforpost-translationalcleavage.Chromograninsareco-storedandco-releasedwithneuropeptidesandhormonesintheneuroendocrinecellsthroughoutthebody.Aroleforchromograninsinthegenerationofhormonalgranulesandpackageofhormoneshasbeensuggested.FurThermore,chromograninscanbecleavedintosmallerfragments,whichcandisplayBIOLOGicalactivitiessuchasinhibitionofhormonalrelease,vasodilatationandanti-microbiologicaleffects.TumoursofneuroendocrineoriginusuallypresentwithincreasedplasmalevelsofchromograninA.Theneuroendocrinetumoursarederivedfromtheneuroendocrinecellsandtypicalneuroendocrinetumoursarecarcinoidtumours,pheochromocytomas,neuroblastomas,smallcelllungcancers,hyperparathyroidadenomas,pituitarytumours,prostatecancersandpancreaticislettumoursandincludingtheMEN1andMEN2syndromes.Thisalsoincludesthedifferentneuroendocrinetumoursyndromes,namelythegastrinomas,insulinomas,glucagonomas,somatostatinomas.PPomasandthenon-functioningneuroendocrinetumours(Eriksson,B.etal.2000).Forthesetumours,chromograninAhasbeenshowntobethebestcirculatingMarker(Bajetta,E.etal.1999).ThefirstrADIoimmunoassayformeasurementsofchromograninAwasintroducedin1986(O’Connor,D.T.&Deftos,L.J.1986).SincethenotherassaysformeasurementsofintacthumanchromograninAhavebeenreported.AssaysformeasurementsofdefinedregionsofchromograninAhavealsobeenestablished,suchasspecificmethodsforpancreastatinandotherregionsofchromograninA(Stridsberg,M.2000).ThepresentchromograninAisacompetitivemethodbasedonpolyclonalantibodiesraisedinrabbits.Theantibodieswereraisedagainstapurifiedfragmentcontainingaminoacidsequence116-439inthechromograninAmoleculeandithasbeenshowntomeasurebothintactchromograninAandfragmentsofchromograninA(Stridsberg,M.etal.1993,Stridsberg,M.etal.1995).