Custom synthetic peptides are valuable reagents in biological research, and are widely used to mimic complex protein structures or antigens. Quality of custom peptides, i.e., purity, is the key to success and integrity of your research. Consequently, the main cost for peptide synthesis is incurred on purification and characterization of custom peptides. We have enlisted some of common applications of synthetic peptides and recommended purity for custom synthesis based on our consultations with experts familiar with these biological assays.