BACKGROUND: Bronchodilation effect of propofol was known that it could prevent bronchoconstriction induced by fentanyl administration. The aim of this study was to investigate the dosage of propofol that inhibited cough reflex induced from fentanyl. METHODS: One hundred twenty patients were randomly allocated to four groups: Group 1 (n=30, fentanyl 3 microgram/kg), Group 2 (n=30, propofol 0.5 mg/kg, fentanyl 3 microgram/kg), Group 3 (n=30, propofol 1 mg/kg, fentanyl 3 microgram/kg), Group 4 (n=30, propofol 2 mg/kg, fentanyl 3 microgram/kg). Patients in Group 1 were injected fentanyl within a second. Other patients groups were injected fentanyl two minutes after administration of propofol dosage, respectively. We checked cough response, oxygen desaturation and chest wall rigidity. RESULTS: There was no significant difference in the incidence of cough response between Group 1 and 2. But, the incidence of Group 3 and 4 was significantly lower than in Group 1 and 2. CONCLUSIONS: Propofol of clinical doses for anesthetic induction inhibit cough reflex induced from fentanyl.