A clinical case of a patient in whom seizure developed after topical application of lidocaine to the oropharyngeal region was described. The exploratory studies on the optimal dosage of lidocaine in the surgery under laryngomicroscope was performed in 22 patients. During the application of 2% lidocaine viscous and 4% lidocaine solution to the oropharyngeal region, the patient was instructed to expectorate the excess intermittently to avoid absorption. In addition, the oropharyngeal region was swabbed with gauze. The serum lidocaine concentrations after application were less than 1.8 μg/ml. The total application dose of the drug was within the range of 324 to 640 mg, and the total recovery rate from the saliva and gauze was 52% to 81%. We found a good correlation between net application dose (total application dose minus excessive lidocaine dose) and serum lidocaine concentration. In this study, it was shown that the safe and effective net application dose of lidocaine for the surgery may be within the range of 127 to 260 mg. Clinical Pharmacology & Therapeutics (1996) 60, 229–235; doi: