Hematologic and serologic studies in 6‐sulfanilamidoindazole arthritis

6‐sulfanilamidoindazole (6‐SAI), an antibacterial sulfonamide, is known to cause an acute, self‐limited inflammatory reaction in the hind paws of older rats. Administration of 6‐SAI results in hyperfibrinogenemia which precedes the onset of clinical arthritis. The hyper‐fibrinogenemia is associated with the prolongation of dilute blood clot lysis times, appearance of heparin‐precipitable fibrinogen, elevations in fibrin degradation products, and complement titers and serum electrophoretic pattern changes that consist of decreased albumin concentrations and increased beta globulin concentrations. Alterations in 6‐SAI medicated young rats are less marked and require higher doses.