We introduce mass spectrometry proteomic research for diagnosis from a clinical perspective, with special reference to early-stage breast cancer detection. The nature of SELDI and MALDI mass spectrometric measurement is discussed. We explain how the mass spectral data arising from this technology may be viewed as a new data type. Some of the properties of the data are discussed and we show how such spectra may be interpreted. Sample preprocessing for mass spectrometry is introduced and a literature review of research in clinical proteomics is presented. Finally, we provide a detailed description of the study design on the breast cancer case-control study which is investigated in this special issue.