Novel biological activities of macrophage migration inhibitory factor (MIF) have been rediscovered. In addition, elevation of the serum MIF level has been reported in different types of disorders, including various inflammatory and autoimmune diseases. In the present study, serum MIF levels were analyzed in patients with Wegener's granulomatosis (WG) and relapsing polychondritis. It was shown that the serum MIF levels in these patients were significantly higher than those of normal healthy controls. In a WG patient, the MIF level showed a good correlation with clinical symptoms and C-ANCA titers. Thus, serum MIF levels will be a useful laboratory parameter for following the clinical course of WG patients and determining medical treatment. The immunopathologic roles of MIF in these diseases are discussed.