The hormonally driven expression and cell-specific localization patterns of the progesterone receptor membrane components (PGRMC1 and PGRMC2) in the macaque endometrium during the menstrual cycle are unknown. Additionally, the expression and localization patterns of PGRMC1 and PGRMC2 in the secretory eutopic endometrium of primates afflicted with endometriosis are also unknown. Therefore, we used real-time PCR to quantify transcript expression levels of the PGRMCs in well-defined samples of endometrium collected from artificially cycled macaques during the menstrual cycle, and in the secretory phase endometrium of naturally cycling macaques afflicted with endometriosis. In situ hybridization and immunocytochemistry were used to localize PGRMC1 and PGRMC2 mRNA and protein, respectively. We compared the patterns of expression and localization of the PGRMCs with the expression and localization patterns of nuclear progesterone receptor (PGR). PGRMC1 and PGR were elevated during the proliferative phases of the cycle, and then declined to nearly undetectable levels during the late secretory phase of the cycle. Levels of PGRMC2 were lowest during the proliferative phases of the cycle and then increased markedly during the secretory phases. Strong staining for PGRMC2 was localized to the luminal and glandular epithelia during the secretory phases. When compared with artificially cycled disease-free animals, macaques with endometriosis exhibited no changes in the expression or localization patterns for PGR and PGRMC1 but exhibited strikingly reduced levels of PGRMC2 transcript and altered intracellular staining patterns for the PGRMC2 protein. Collectively, these results suggest that membrane-bound PGRMC2 may provide a pathway of action that could potentially mediate the non-genomic effects of progesterone on the glandular epithelia during the secretory phase of the cycle. Further, reduced levels of membrane-bound PGRMC2 may be associated with the progesterone insensitivity often observed in the endometrium of primates afflicted with endometriosis.