We have previously shown that human epidermal keratinocytes express macrophage migration inhibitory factor (MIF) mRNA, and immunohistochemical studies showed that MIF is expressed in human epidermis. To explore the possible pathophysiological roles of MIF in skin during rat fetal development, we examined the expression patterns of MIF during rat epidermal development using Northern blot analysis and in situ hybridization. Expression of MIF mRNA was first detected by in situ hybridization in the developing epidermis and hair germ cells from embryonic day (ED) 16. From ED 19, moderate levels of MIF expression were detected in the epidermis and epithelial sheath cells of growing hair follicles. In postnatal rat skin, higher MIF expression was detected in the epidermis and hair follicles on postnatal day 3. These observations were also confirmed by Northern blot analysis. Immunohistochemical analysis with an anti-MIF antibody showed a similar distribution to that of the mRNA. Our results suggest that MIF is associated with epidermal and hair follicle development.