['To assess pinopode formation in Lif null and Hoxa10 null mice with infertility secondary to failed implantation.', 'Controlled animal experiment.', 'Animal research and laboratory facility.', 'Lif null, Hoxa10 null, and ICR mice and Sprague-Dawley rats.', 'Endometrial tissue was collected during the peri-implantation period and after ovariectomy.', 'Endometrial epithelial tissue was examined under scanning-electron microscopy and assigned a score depending on the number of pinopodes present.', 'Pinopode scores in ICR, Lif null, and Hoxa10 null mice were comparable throughout the peri-implantation period, rising on day 3.5 of pregnancy and remaining elevated through to day 7.5, suggesting that pinopodes are not a good indicator of receptivity in mice. In contrast, pinopode scores in rats clearly demarcated the window of receptivity, appearing on day 4 of pregnancy and declining sharply on day 6. Pinopode scores were low in E(2)-treated ovariectomized mice, but unexpectedly, pinopode scores in vehicle-injected ovariectomized ICR mice were markedly elevated.'] Are pinopodes present in Lif null and Hoxa10 null mice?