Analysis of rheumatoid factor (RF) effects according to physiological principles suggests that RF activity may decrease joint swelling by (i) decreasing synovial fluid (SF) colloid osmotic pressure, by increasing plasma viscosity and thereby decreasing (ii) fluid escape from the plasma and (iii) convective flux of proteins into joints, and by decreasing (iv) diffusion of proteins from capillaries (et cetera?). RF complexes raising whole blood viscosity might (v) decrease blood flow. A more significant cause of SF hypoxia and lactic acidosis may be tamponade of synovial circulation created by swelling-induced high SF hydrostatic pressures. Increase of non-RF IgG or monomeric IgM and possibly agammaglobulinaemia could contribute to swelling more strongly than RF's.