[Serological profile in so-called seronegative rheumatoid arthritis]

89 cases of sero-negative rheumatoid arthritis (RA) were compared to 127 cases of sero-positive RA. Anti-perinuclear and anti-keratin antibodies were detected less frequently in the first group (51 vs 67% and 28 vs 33%, respectively), while the inverse was found for anti-nuclear antibodies (28 vs 24%). "Light" rheumatoid factors (RF)--IgG, IgM, IgE, IgA and IgD--were detected in 23.6, 21.3, 17.5, 11.3 and 0 per cent of cases of sero-negative R.A. The evolutive state of these cases was less severe. RF agglutinins were detected in 5 out of 12 samples of synovial fluid tested in cases of sero-negative RA.