Macrophage migration inhibitory factor (MIF) was the first lymphokine identified in activated T-lymphocytes. MIF can induce proinflammatory cytokines, such as interleukin-1 and tumor necrosis factor-alpha. In this study, we identified MIF expression in a tissue specimen of a normal portion of a nephrectomized human kidney by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. Furthermore, immunohistochemical study using an anti-human MIF polyclonal antibody demonstrated that MIF was mostly present in the renal tubule epithelial cells and, to a lesser extent, in Bowman's capsular epithelial cells. We also carried out immunohistochemistry on cultured human renal proximal tubule epithelial cells, which showed that MIF was present in the cytoplasm of the epithelial cells. These results suggest the possibility that MIF takes part in the mechanism of inflammation and immunological events in the human kidney.