Uterine epithelial cells from normal human endometrium were cultured as a primary cell culture in a dual-chambered system. The epithelial cells were isolated from endometrial tissue of the proliferative phase obtained by hysterectomy. The epithelial cells were seeded on Millicell CM filters coated with the extracellular matrix Matrigel. Depending on the culture conditions, the epithelial cells formed a polarized cell monolayer on Matrigel or gland-like structures in Matrigel. The epithelial cell polarity was maintained during culture, which could be proved by electron microscopy. The progesterone and estrogen receptors as typical marker molecules for physiologically intact endometrial epithelial cells could be detected immunohistochemically as well as by RT-PCR in vitro and were down-regulated by medroxyprogesterone acetate (MPA) used as progesterone analogue. As this cell culture system exhibits morphological and immunohistochemical characteristics, typical for the in vivo situation, and since it can be modulated by hormone treatment under the in vitro conditions described, it represents a valuable tool for investigating processes that are essential for endometrial differentiation and reproductive functions.