We have previously shown that gap junctions and gap junction-associated protein connexin 43 are present in the human and baboon corpus luteum. Abundant expression of connexin 43 is seen in the midluteal phase corpora lutea. Since the formation of gap junctions requires the presence of adherens junctions formed by the cadherins, our aim in these studies was 1) to immunocytochemically localize E-cadherin and the associated proteins, beta-catenin and gamma-catenin (plakoglobin), in the baboon corpus luteum; 2) to determine by Western analysis the levels of these proteins in early, mid-, and late luteal phase and atretic baboon corpora lutea; and 3) to examine whether or not cell-cell contact in cells in culture is disrupted by the addition of the antibody for E-cadherin. E-cadherin was localized to the peripheral cell membranes of luteal cells at all stages examined, except atretic corpora lutea, with the strongest immunoreactivity in the early luteal phase. Both beta-catenin and plakoglobin were localized in the cytoplasm of the luteal cells. Immunoreactivity for all three peptides was not observed in nonluteal tissue. By Western analysis, abundant expression of E-cadherin was observed in the early luteal phase, and the level of expression was significantly different from that observed in the mid- and late luteal phase corpora lutea. In contrast, the levels of beta-catenin and plakoglobin were higher in the midluteal phase compared to the early luteal phase. Addition of the E-cadherin antibody to early luteal phase cells in culture disrupted the cell-cell contacts between cells. Thus, cell adhesion involving E-cadherin may play a significant role in the cyclic development and demise of this tissue.