A putative membrane bound steroid receptor was localized using a peptide specific antibody. Surprisingly, the distribution of immunocytochemical staining in porcine hepatocytes cells provides evidence for the localization to endomembranes (endoplasmic reticulum, Golgi apparatus). Immunofluorescence experiments with HEK cells, which were transfected with a pcDNA3.1 vector containing the coding sequence of the putative progesterone binding protein shows staining within the cells supporting these results. Additionally, 3H-progesterone binding and glucose-6-phosphatase activity as marker enzyme for endoplasmic reticulum were closely correlated in subcellular fractions of porcine liver cells.