The aim of the study was to evaluate the cardiorespiratory and clinical effects of propofol and remifentanil anesthesia compared to propofol and fentanyl anesthesia during ovariohysterectomy in dogs. Sixteen healthy dogs were randomly assigned to two groups. After premedication with atropine, anesthesia was induced with propofol and maintained with the infusion of propofol at a dose of 0.5 mg/kg/min. Once stable anesthesia was achieved, 1 mu g/kg remifentanil or 2 mu g/kg fentanyl was administered intravenously, and infusion was begun at a dose of 0.6 mu g/kg/min and 0.5 mu g/kg/min, respectively. Cardiorespiratory variables were recorded after propofol administration combined with remifentanil or fentanyl at 10-min intervals, and the quality of anesthesia, return of spontaneous ventilation, head lift and sternal position were also recorded. Apnea was observed after remifentanil and fentanyl administration in all dogs. Heart rate, systolic and mean arterial blood pressures tended to decrease rapidly after remifentanil and fentanyl administration, and during the first 20 min, in both groups. Although the difference between times was significant, the difference between groups was statistically insignificant. Recovery periods were longer in the fentanyl group than in the remifentanil group. The administration of propofol with remifentanil or fentanyl provides a stable haemodynamic state and depth of anesthesia with a constant infusion, and remifentanil could be preferred to fentanyl when aiming a rapid recovery period.