Updated project metadata. In the present study, synovial fluid (SF) samples from inflammatory arthritis (IA) patients were subjected to a label-free, mass spectrometry-based approach for the identification and quantification of IA-specific proteins and peptides. The discovery-phase project generated a warehouse of proteomic and peptidomic data providing a basis for the identification of candidates with the greatest potential to serve as novel biomarkers specific to inflammatory arthritides. A total of 11 protein candidates and 15 peptide candidates, originating from 4 proteins, were selected for follow-up studies.