Peptidomics is defined as a 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 served as a complement strategy to bridge the gap between proteomics and metabolomics. The 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 likely from disease-specific proteolytic cleavage.