ABSTRACTIn this study, female canines referred with clinical signs consistent with pyometra were prospectivelyevaluated. Signalment, clinical signs, laboratory findings and surgical findings werecompared between dogs with and without bacterial isolation based on aerobic techniques. Patientswith positive bacterial isolation were placed in the pyometra group, whereas patients withnegative bacterial isolation were grouped as mucometra. A total of 140 dogs (118 with pyometraand 22 with mucometra) met the inclusion criteria.Prereferral antibiotic administration was associated with a prolonged duration of clinicalsigns in the patients of the pyometra group (12 ± 2 days versus 7 ± 1 days; P=0.006). In the pyometrapatients, clinical signs, like pyrexia, anorexia and discomfort on abdominal palpation,were observed more commonly than in the mucometra group. The total leukocyte count wasthe only parameter that differed significantly between the two groups (P=0.01). Although no differencein color and consistency of the uterine fluid was noted, the uteri of the pyometra groupwere heavier (851.80 ± 800.30 g compared to 263.50 ± 297.10 g). E. coli was the most commonlyisolated bacterium (92/123).