Gout and classical rheumatoid arthritis rarely coexist. We report a patient with strong evidence for both these diseases. Possible reasons for the negative correlation between these diseases are summarised. One hypothesis suggests inhibition of surface activity of monosodium urate crystals (MSU) by binding of rheumatoid factor (RF). This was studied with a purified monoclonal rheumatoid factor (mRF) with specificity for IgG. The mRF bound preferentially to MSU coated with IgG in contrast with the IgM control. Inhibition of the neutrophil chemiluminescence (CL) response to IgG-coated MSU was observed at concentrations of mRF that had no effect on the CL response to uncoated crystals. Neutrophil activation was not altered by coating crystals with an IgM control at the same concentration. These data suggest that RF may bind to antigenic determinants on exposed Fc of adsorbed IgG and block the interaction of crystal-bound IgG with Fc receptors. Although crystal coating by RF may modify the expression of gouty arthritis, it is unlikely to be the sole explanation for the dissociation between gout and RA.