Pyometra, chronic purulent metritis in metoestrus, is a common disease in intact bitches. About 25% of all bitches in Sweden have contracted the disease before ten years of age. Clinical signs of the disease are varied, and the course may be either slow or acute. The diagnosis is most commonly made by radiographical or ultrasonographical examination of the abdomen in combination with blood biochemical and hematological analyses. The safest and most efficient treatment of pyometra is surgical ovariohysterectomy.There is room for improvement of both diagnostic tools and possible prognostic indicators for pyometra.Mast cells are large leucocytes, with granule that contain inflammatory mediators.