Peptidomics is defined as the systematic, comprehensive, qualitative/quantitative multiplex analysis of endogenous peptides (up to ~20 kDa), in biological samples collected at a chosen time point and location. Peptidomics can complement proteomics and bridge the gap between proteomics and metabolomics. And invaluable information can be obtained from studies of the numerous soluble polypeptides, including signaling molecules (such as cytokines, growth factors, and peptide hormones), and other small protein fragments and peptides of undetermined functions, or from disease-specific proteolytic cleavage.