Canine pyometra, one of the most important pathologic conditions of the canine uterus, is frequently accompanied by endometrial glandular hyperplasia and cystic transformation of the endometrial gland (cystic endometrial hyperplasia – CEH). TNF (Tumor Necrosis Factor), a pleiotropic inflammatory cytokine, has been identifiedin the uterus os several species ans its expression was shown to change in some pathological conditions. The aim of this study was to evaluate TNF immunoexpression in canine endometrium with CEH/pyometra,and to compare it with late postpartum and control samples from ddifferent stages of the canine oestrus cycle.