Despite a battery of tests available for diagnosing periprosthetic joint infection, as yet, no gold standard has been identified. Our purpose was to measure inflammatory proteins in synovial fluid from patients undergoing revision arthroplasty for septic or aseptic failure. We analyzed 74 synovial fluid samples: 31 infected and 43 uninfected, based on clinical and laboratory criteria. Proteomics analysis and receiver operating characteristic curve analyses were conducted on 46 inflammatory proteins for each sample. Of 46 proteins, 5 (interleukin 6, interleukin 8, α 2-macroglobulin, C-reactive protein, and vascular endothelial growth factor) had an area under the curve greater than 0.90. This prospective study has demonstrated promising results for the use of molecular markers in diagnosis of periprosthetic joint infection. Future studies will focus on designing assays with these proteins in mind.