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Study Objective: To investigate whether the type of anesthetic agent administered affects the antitussive effect of remifentanil. Design: Prospective randomized study. Setting: Operating room of a university hospital. Patients: 78 ASA physical status 1 and 2 women, aged 20 to 65 years, who were scheduled to undergo a thyroidectomy. Interventions: Patients were randomly assigned to three groups to receive anesthesia with propofol (Group P), sevoflurane (Group S), or desflurane (Group D). The main anesthetics were titrated to maintain a target Bispectral Index for hypnosis of 40 to 60. Remifentanil was administered via effectsite target-controlled infusion (TCI). To determine the effective remifentanil effect-site concentration (Ce) to suppress coughing in each group, the up-and-down sequential allocation design was used. Measurements: The half maximal effective concentration (EC50) values of remifentanil for preventing coughing in the groups were estimated using isotonic regression and compared among the groups. Main Results: The EC50 of remifentanil for cough suppression in Group P [1.60 ng/mL (98.3% CI, 0.92 - 1.75 ng/mL)] was statistically lower than in Group D [1.96 ng/mL (98.3% CI, 1.81 - 2.50 ng/ mL)]. The EC50 in Group S was 1.75 ng/mL (98.3% CI, 1.39 - 2.13 ng/mL), which was higher than in Group P and lower than in Group D, but did not differ significantly from either group. Conclusions: Remifentanil administration for cough suppression during emergence should be customized to the anesthetic agent. [ABSTRACT FROM AUTHOR]