Endometrial glandular epithelial cells were subcultured on matrix-coated filters in bicameral chambers in a serum-free chemically defined medium. The cells were untreated or treated with 50 nmol progesterone l-1 or 10 nmol oestradiol l-1 or 10 nmol oestradiol l-1 plus 50 nmol progesterone l-1 and the proteins secreted into the basal or apical compartment were analysed after [35S]methionine labelling. Compared with the untreated cells, oestradiol treatment did not affect the electrophoretic profiles of proteins secreted by the glandular epithelial cells in either compartment. Progesterone treatment induced a decrease in the labelling of 88 and 53 kDa proteins secreted in the apical and basal compartments and an increase in the labelling of a 28 kDa protein. Moreover, progesterone specifically induced the apical secretion of a 137 kDa protein. Interaction between the epithelial and stromal cells was also investigated. When stromal cells were cultured in the basal compartment under the epithelial monolayer, the progesterone effect on the apical secretion of the 137 kDa protein and basal secretion of the 88 and 28 kDa proteins were altered, whereas this progesterone effect was not altered when the epithelial cells were cultured alone in media conditioned with stromal cells. Interactions between epithelial and stromal cells modified the effect of progesterone on protein secretion by the epithelial cells.