BACKGROUND: Propofol and lidocaine have been purported to attenuate bronchoconstriction induced by fentanyl administration during induction of anesthesia. The purpose of the present study was to study the synergic bronchodilation effect of propofol mixed with lidocaine. METHODS: Two hundred and thirty four patients were randomly allocated to five groups: Group 1 (n = 60, normal saline 0.25 ml/kg followed by fentanyl 3ng/kg), Group 2 (n = 30, propofol 2 mg/kg mixed with normal saline 0.05 ml/kg followed by normal saline 0.06 ml/kg), Group 3 (n = 50, propofol 2 mg/kg mixed with normal saline 0.05 ml/kg followed by fentanyl 3ng/kg), Group 4 (n = 33, propofol 2 mg/kg mixed with lidocaine 1 mg/kg followed by normal saline 0.06 ml/kg) and Group 5 (n = 61, propofol 2 mg/kg mixed with lidocaine 1 mg/kg followed by fentanyl 3ng/kg). All patients were injected with fentanyl or normal saline two minutes after administration of propofol premixed with lidocaine or normal saline, respectively. We checked the cough reflex, injection pain, oxygen desaturation and chest wall rigidity. RESULTS: There was a significant difference in the incidence of cough reflex between group 1 and 3 or 5. The incidience of group 5 was significantly lower than in group 3. CONCLUSIONS: This study suggests that a propofol-lidocaine mixture should be considered when patients require bronchodilation during induction of anesthesia.