Fentanyl and ketamine are often used as adjuvants in intravenous anaesthesia to prolong analgesia. The aim of this study was to compare changes of the basic physiological variables of intravenous lidocaine administration in combination with ketamine or fentanyl, and to evaluate the impact of addition of fentanyl or ketamine to lidocaine on serum lidocaine concentrations in dogs after intravenous administration. During general anaesthesia, dogs of group L received 2% lidocaine intravenously, dogs of group LF received 2% lidocaine and fentanyl, and dogs of the group LK received 2% lidocaine and ketamine. The heart rate, systolic arterial pressure, diastolic arterial pressure, mean arterial pressure and rectal temperature decreased in all groups, and group LF showed the biggest effect on the basic physiological variables, with the lowest heart rate during the test, significantly decreased rectal temperature, and the most decreased values of arterial pressure. Blood for determination of serum lidocaine concentration was taken before anaesthesia and 5, 30, 60, 90, 120, 150 and 180 min after initial intravenous injection of drugs. Fentanyl and ketamine did not cause significant changes of serum lidocaine concentration in dogs and may be used as adjuvant in intravenous anaesthesia without a significant increase in lidocaine absorption.