We studied the usefulness of the 10 mg presentation of vecuronium bromide (NC45-10) for endotracheal intubation. Subjects were ASA type I-II patients between 20-65 years of age scheduled for various kinds of surgery who consented to participate in this study. After the entrance of patients into the operating room, we set up monitors and intravenously injected a priming dosage of NC45-10, 0.015 mg.kg-1. Next, we administered thiopental 5 mg.kg-1 and injected initial dosage of either 0.065 mg.kg-1 or 0.1 mg.kg-1 of NC45-10 intravenously 5 minutes after the administration of priming dose. One minute later, we attempted endotracheal intubation. We evaluated the muscle relaxation by the reaction to endotracheal intubation and graded it by the score of 0-3. Satisfactory muscle relaxation on endotracheal intubation was obtained in 80% of the patients with no significant difference between the 2 groups of initial dosage. No side effect or cardiovascular action was observed. It is concluded that this preparation is clinically safe and useful.