The main findings of this work are: (i) the validation of serum Gal1 measurement as a possible diagnostic biomarker for RA; and (ii) the presence of even higher levels of this molecule in synovial fluid from patients with RA, as well as in comparison with synovial fluid from other mechanic or inflammatory processes such as osteoarthritis and microcrystalline arthritis. This evidence concerns the gene LGALS1 and rheumatoid arthritis.