The effects of fentanyl on arterial pressure and heart rate increases during laryngoscopy and intubation were studied in 45 normotensive, surgical patients, who were randomly allocated to three groups receiving 2 or 6 micrograms/kg of fentanyl or saline in a double-blind fashion before anaesthetic induction with thiopental. Fentanyl supplementation with 2 micrograms/kg significantly attenuated the arterial pressure and heart rate increases during laryngoscopy and intubation, and fentanyl, 6 micrograms/kg, completely abolished these responses. Moreover, fentanyl given during the induction decreased the amount of fentanyl needed during the operation. Respiratory depression was not observed during recovery.