The immunoglobulin heavy chain binding protein BiP(GRP78), or a fragment thereof, provides a reagent for indicating the presence of rheumatoid arthritis (RA). The protein used is a recombinant BiP(GRP78) having a defined sequence. A prognostic and/or diagnostic test for RA may be an ELISA or a Western Blot that utilizes the BiP(GRP78) protein or a fragment thereof. Also disclosed are a method of testing for RA using BiP(GRP78) or a cDNA sequence coding therefor. Further disclosed is a method of treating RA by the BiP(GRP78) protein or corresponding cDNA.