Eosinophils, macrophages and other leucocytes invade the uterine endometrium during oestrus and play a role in the tissue remodeling and immune responses that occur prior to implantation of the fertilized ovum. Adenosine 5'-triphosphate (ATP) and its metabolites influence uterine function via ATP receptors. In this study, we investigated the presence and localisation of the P2X(7) nucleotide receptor in the cells that infiltrate the uterine endometrium of adult female rats during oestrus at the electron microscope level, using gold-silver pre-embedding immunocytochemical techniques. P2X(7) receptor expression was found in the cytoplasm and the cell membrane of eosinophils, macrophages and fibroblasts in the endometrium during oestrus. These results suggest that ATP-mediated responses may be important in uterine preparation and remodeling before implantation and that this may involve several types of cells. In particular, the presence of P2X(7) receptors on endometrial stromal cells may indicate their involvement in apoptosis and immune and inflammatory responses.