QConCAT is a method for multiplexed absolute quantification in proteomics using concatenated signature peptides encoded by QConCAT genes. There are three main steps in the QConCAT informatics workflow: 1) selection of unique QConCAT peptides for the target proteins, 2) analysis and submission of mass spectrometry data to identify the QConCAT peptides and generate concentration ratios, and 3) browsing and querying the quantitative proteomics data stored in a searchable repository.