Two　online　sample　stacking　methods　in　capillary　electrophoresis,　large　volume　sample　stacking　using　reversed　pressure　as　a　pump　(LVSRP)　and　large　volume　sample　stacking　using　electroosmotic　flow　(EOF)　pump　(LVSEP),　were　developed　for　the　separation　and　determination　of　carnosine,　anserine,　and　homocarnosine.　The　principles　of　the　two　stacking　methods　were　described.　Various　parameters　affecting　capillary　electrophoresis　separation　and　sample　stacking　were　studied　and　optimized.　The　optimal　stacking　conditions　for　LVSRP　were　as　follows:　hydrodynamic　sample　injection　at　41.4　kPa　(60　s),　then　injection　of　a　short　plug　of　buffer　at　13.8　kPa　×　15　s,　stacking　of　sample　at　a　voltage　of　10　kV　with　a　back　pressure　of　34.5　kPa,　and　separation　in　phosphate　buffer　(pH　5.63,　100　mmol/L)　at　a　voltage　of　15　kV.　The　optimal　stacking　conditions　for　LVSEP　were　as　follows:　hydrodynamic　sample　injection　at　48.3　kPa　(60　s),　and　stacking　and　separation　in　a　buffer　of　100　mmol/L　phosphate-0.5　mmol/L　cetyltrimethylammonium　bromide　(CTAB)　(pH　5.31)　at　a　voltage　of　20　kV.　About　40-60　fold　improvement　of　sensitivity　was　achieved　without　loss　of　separation　efficiency　by　LVSRP　and　LVSEP,　compared　with　the　normal　CZE　method.　Under　the　optimum　conditions,　excellent　linear　responses　were　obtained　in　the　concentration　range　of　0.080-5.0　μmol/L　with　the　correlation　coefficient　ranging　from　0.9962　to　0.9999.　The　relative　standard　deviations　(RSDs)　of　peak　height　were　2.4%-2.7%　and　0.6%-4.0%　for　LVSRP　and　LVSEP,　respectively.　The　concentration　limits　of　detection　(defined　as　the　signal-to-noise　ratio　of　3)　of　carnosine,　anserine,　and　homocarnosine　obtained　for　LVSRP　and　LVSEP　were　41-58　nmol/L　and　35-43　nmol/L,　respectively.　©　2007　Chinese　Chemical　Society　and　Dalian　Institute　of　Chemical　Physics,　Chinese　Academy　of　Sciences.