A new procedure for labeling hydroxyapatite (HA) particles with ¹⁸⁸Re for radiation synovectomy is described and standardized. The particles were labeled with ¹⁸⁸Re in high yields (99%) in acidic medium. HA particle size remained unaffected by reaction conditions as checked by laser diffraction particle analyzer. ¹⁸⁸Re-HA was found to be stable retaining 99% radiochemical purity after 4 days when stored in ascorbic acid solution (10 mg/ml, pH 5). Intra-articular injection in rats revealed ~98% retention of ¹⁸⁸Re-HA in the knee after 48-h pi.