Tracheal intubation may be accomplished with remifentanil and a non-opioid IV anesthetic without a muscle relaxant. In this study, we evaluated in double-blinded, prospective, randomized manner the dose requirements for remifentanil with thiopental without muscle relaxant administration to obtain clinically acceptable intubation conditions and cardiovascular responses. After premedication with midazolam 0.03 mg/kg IV, 105 patients were randomized equally to one of three study groups, each receiving the following: remifentanil 2 mug/kg (Group 1), 3 mug/kg (Group 11), and 4 mug/kg (Group Ell). Remifentanil was administered over 30 s, and anesthesia was induced with thiopental 5 mg/kg. Tracheal intubation conditions were assessed by the anesthesiologist performing the intubation as: (a) excellent, (b) satisfactory, (c) fair, and (d) unsatisfactory. There were no statistically significant differences among groups regarding to demographic data. Blood pressure and heart rate did not increase in any group after accomplishing intubation. There was a significant improvement in intubation conditions between Groups I and 11, 1 and 111, and II and III (P < 0.001). We conclude that remifentanil 4 mug/kg administered before thiopental 5 mg/kg provided excellent or satisfactory intubation conditions in 94% of patients and prevented cardiovascular responses to intubation.