Anaphylaxis or anaphylactoid reactions rarely occur during the perioperative period but can be a devastating complication of general anesthesia. We experienced a patient with an unexpected anaphylaxis. A 11-yr-old boy was scheduled for extraction and treatment of caries under general anesthesia. Ketamine, thiopental sodium and rocuronium were used for induction of anesthesia. After induction lidocaine was injected through oral mucosa for pretreatment. About 3 minutes later hypotension, tachycardia, bronchoconstriction and reddish skin eruptions developed. The operation was put off and skin prick test for screening the contributing drug was performed. Lidocaine reacted positively to the test. Based upon the result, second operation could be performed safely and successfully without using lidocaine.