Microparticles derived from platelets (CD61) and erythrocytes (glycophorin A) were below detection level (less than 107/l) in synovial fluid from all patients, except in one RA patient who had a low but detectable number (1.7 × 107/l) of platelet-derived microparticles. The gene discussed is ITGB3; the disease is rheumatoid arthritis.