Currently, the main focus of clinical proteome analysis is on detection and identification of polypeptides that significantly change owing to pathological changes. Capillary electrophoresis coupled online to an electrospray ionization time of flight mass spectrometer (CE-MS) allows the differential display of a large number of polypeptides in a single, reproducible, and time-limited step and enables the comparison of different protein profiles for biomarker discovery. In addition to the reproducibility of the CE-MS setup, many further steps including data processing and mining, usage of biomarkers for diagnosis, and biomarker sequencing are necessary to answer the demands of biomarker discovery of clinical significance. In this chapter, we discuss materials and methods for CE-MS-based clinical proteomics allowing the reproducible profiling of urine.