In mammals, the purpose of the estrous cycle is the successful progression of implantation and pregnancy. The endometrium undergoes several changes during the estrous cycle. The extracellular matrix proteins have a likely role in the maintenance of a healthy endometrium. In this study, we investigated the localization of the fibronectin receptor (Integrin beta(1)), a member of the integrin family, and laminin, an extracellular matrix protein, in the bitch uterus throughout the estrous cycle. In the bitch uterus, immunoreactions of similar intensity were observed for the fibronectin receptor (Integrin beta(1)) in the myometrium, perimetrium, peritoneal mesothelial cells and uterine vasculature, and for laminin in the peritoneal mesothelial cells, throughout the estrous cycle. Laminin and the fibronectin receptor (Integrin beta(1)) were found to be present at high intensity in the endometrium of the bitch uterus at the luteal stage.