In this study, the suitability of SPE coupled on-line to CE-electrospray-MS (SPE-CE-ESI-MS) was evaluated for the analysis of neuropeptides in human plasma. First, CE-ESI-MS was investigated and a sample pretreatment based on precipitation with ACN was used for cleanup of plasma samples. The main quality parameters were determined and were consistent with those previously obtained for the analysis of standard mixtures, e.g., the LODs were of around 1 mu g/mL. SPE-CE-ESI-MS employing microcartridges containing a C18 stationary phase was explored in order to decrease the LODs. A double-step sample cleanup pretreatment consisting of precipitation with ACN and ultrafiltration through 3000 Da MW cut-off membranes was needed to prevent the microcartridge saturation. Repeatability, reproducibility, linearity, and LODs of the SPE-CE-ESI-MS method and the durability of the microcartridges were studied. The LODs were markedly improved, ranging between 1.0 and 0.1 ng/mL depending on the peptide.