Intact rat external ear canal explants were maintained either in retinoid-deficient or retinoid-supplemented medium for 7, 10, 14, and 21 days. The morphology of the external ear canal epidermis was well maintained, including the presence of sebaceous glands even after 21 days in culture with retinoid-deficient medium. However, after culturing in retinoid-supplemented medium, the external ear canal epithelium showed both a loss of keratohyalin granules and the formation of keratin. Extensive microvilli formation occurred, even though the desquamation process continued from the superficial layer after 7, 10, and 14 days in culture with retinoid-enriched medium. After 21 days in culture with retinoid-supplemented medium, the ear canal epithelium contained well-developed Golgi apparatus and secretory granules as well. It was concluded that the ear canal epithelium was transformed into a secretory-like mucosal epithelium by retinoid supplementation.