The successful coupling of capillary electrochromatography (CEC) to an ion trap mass spectrometer via a nanoelectrospray interface (nESI) is described. Using a conductively coated tip butted to the end of a CEC column, it was possible to obtain a stable spray without any sheath liquid being employed. Selected small peptides were separated with CEC columns (100 μm i.d./25 cm long) packed with 3 μm Hypersil C8 or C18 bonded silica particles with an eluent composed of ammonium acetate/acetonitrile. Peptide mixtures of desmopressin, peptide A, oxytocin, carbetocin and [Met5]-enkephalin were detected in the mid-attomole range, which is the lowest amount analyzed using CEC combined with MS detection. It was also observed that sensitivity can be compromised at higher separation voltages. We demonstrate that CEC/nESI-MS, at the current stage of development, represents one of the most sensitive systems for peptide analysis. Copyright (C) 2000 John Wiley and Sons, Ltd. Chemicals/CAS: carbetocin, 37025-55-1; Desmopressin, 16679-58-6; Enkephalin, Methionine, 58569-55-4; Oncogene Protein pp60(v-src), EC 2.7.1.112; Oxytocin, 50-56-6; peptide A; Peptide Fragments; Peptides