Background/Aim: The processes involved in development of IgA nephropathy (IgAN) are not yet well understood. Macrophage migration inhibitory factor (MIF) is a potent pro-inflammatory cytokine and is an essential component of immune and inflammatory responses. To examine further the possible role of MIF in IgAN, we measured MIF levels in the urine. The purpose of the present study was to evaluate the involvement of MIF in IgAN. Methods: Urine samples were obtained from 20 IgAN patients. The disease controls included 20 patients with minimal-change nephrotic syndrome (MCNS). A group of healthy subjects served as control. The samples were assayed for MIF protein by a sandwich enzyme-linked immunosorbent assay (ELISA). Results: The MIF levels in the urine of patients with IgAN examined were significantly higher than those of the healthy control subjects. In contrast, the levels of urinary MIF (uMIF) in patients with MCNS did not differ significantly from normal values. In IgAN patients, uMIF significantly correlated with the magnitude of proteinuria, but not with the grade of hematuria. We also investigated the relationship between uMIF levels and pathological features. Among patients with IgAN, uMIF levels were significantly correlated with the grade of glomerular crescent formation and that of mesangial cell proliferation. There was also a significant correlation between uMIF levels and the number of both intraglomerular and interstitial macrophages. Conclusion: Although the underlying mechanisms remain to be determined, these data provide evidence that urinary excretion of MIF is increased in IgAN patients with active renal lesions.