Pyometra is a common reproductive disorder that affects approximately 25% of intact bitches of older age. The clinical signs are associated with inflammation and uterine infection, and generally include polyuria, polydipsia, anorexia, dehydration and fever. These abnormalities can cause electrolytic and acid-base disturbances and rapidly evolve to sepsis and septic shock. The aim of this study was to describe the acid-base patterns of a small series of dogs with pyometra. We conducted a retrospective a survey of dogs admitted at the intensive care unit of the Pompéia Veterinary Hospital, with a presumptive diagnosis of pyometra, based on clinical signs, leukogram compatible with inflammatory or infectious process, and sonographic evidence of pyometra, during the period of February, 2008 to January, 2009. For this study were selected only those dogs whose diagnosis of pyometra was confirmed during surgery and measurement of blood lactate, bicarbonate, and pH were performed before surgery, totaling 16 animals. Venous blood for laboratory analysis was collected after volume replacement with Ringer's solution. Blood samples were analyzed with the I-STAT Portable Clinical Analyzer. Of these, 50% (8/16) had pH within the reference range (7.35-7.45), 31% (5/16) had acidemia, and 19% (3/16) alkalemia. In 56% (9/16) of the dogs have metabolic acidosis (values of bicarbonate < 19 mEq/L), 37.5% (6/16) had blood bicarbonate within the reference range (19-24 mEq/L), and one dog had a bicarbonate concentration above 25 mEq / L, suggesting metabolic alkalosis. Most of the dogs (12/16 [75%]) had lactate values were within normal values (< 2.5 mmol / L) and 25% of the dogs (4/16) had increased lactate. We conclude that, although half of the patients have a blood pH within reference range, blood gases assessment is an important part of care of dogs with pyometra because of the unpredictable acid-base abnormalities that can occur, and a larger sample should be evaluate to further investigate the occurrence of hidden mixed acid-base disturbances.