We aimed to assess the usefulness of monitoring inter-alpha trypsin inhibitor heavy chain 4 (ITIH4) and haptoglobin (Hp) in peripheral and local blood in canine pyometra, and evaluation the relationships among acute phase proteins (APPs), systemic inflammatory response syndrome (SIRS) and the presence of bacteria. The material was collected from bitches with pyometra and from healthy ones. Blood was taken from the cephalic and uterine veins. APPs levels were quantified by ELISA. In the peripheral circulation, the Hp was higher in animals with open-cervix pyometra (OCP) than in the closed-cervix pyometra (CCP) and the control group. The Hp concentration was not correlated with age, with the presence of SIRS or with the type of bacteria (Gram-negative, Gram-positive or mixed flora). The ITIH4 concentrations in the peripheral blood did not differ significantly in the cases of pyometra. The Hp concentration in the local circulation increased in the OCP but not in the CCP groups, although the histopathological changes in the endometrium were similar. Peripheral Hp concentrations may be a useful tool in differentiating between the types of pyometra.