A　new　method　for　the　determination　of　the　peptide　hormones　of　brain　and　intestine　based　on　CE　coupling　with　a　DAD　and　ESI-MS　was　established.　Several　electrophoretic　and　ESI-MS　parameters　were　investigated　in　detail,　such　as　electrolyte　nature　and　concentration,　organic　solvent　and　sheath　liquid　compositions,　nebulization　gas　pressure　and　the　ESI　capillary　voltage.　Optimized　conditions　were　achieved　with　25　mM　formic　acid-ammonium　formate　(pH　2.9)　as　the　optimal　electrolyte,　2　mM　formic　acid　in　80%　methanol　in　water　as　the　sheath　liquid,　and　20　kV　applied　voltage.　Under　the　optimized　conditions,　four　protonated　peptides　were　separated　by　CE　and　selectively　detected　by　a　quadrupole　mass　spectrometer　with　a　sheath　flow　ESI　interface.　LODs　for　the　four　peptides　(neurotensin　hexapeptide,　neurotensin,　cholecystokinin　tetrapeptide,　and　pentagastrin)　were　in　the　range　of　0.10-0.60　μmol/L　at　an　S/N　of　3.　The　RSDs　(n　=　8)　of　the　method　were　0.70-1.5%　for　migration　times　and　1.6-6.1%　for　peak　areas.　This　method　is　simple,　rapid,　and　selective　compared　with　RIA　and　ELISA　techniques,　and　has　been　applied　to　the　analysis　of　rat　hypothalamus　tissue.　©　2007　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim.