Rat hypophyseal intermediate lobe cells, partially dispersed by trypsin, were cultivated on an inert surface. The attaching capacity, the growth of the cultures and the fine structure of the epithelial cells developed during cultivation were studied. The majority of the cell groups attached to the inert surface within 72 h after explantation. Epithelial islands developed, with a layer consisting of fibroblast-like cells beginning to form at their periphery. By the end of the second week of cultivation the epithelial islets and fibroblast-like cells formed a monolayer. The epithelial cells survived for five weeks. The granular cytoplasm of the epithelial island cells could be well identified on the phase-contrast microcinematographic frames of the young cultures; both epithelial and fibroblast-like cells divided. The mitotic ability of both cell types could be confirmed by their tritiated-thymidine incorporation, too. In young cultures, the fine-structural features of epithelial cells were practically identical with those of the glandular cells in intact glands. In older cultures, the secretory granules in the epithelial cells were lower in number; the localization of the granules at the periphery was predominating.