A 37-year-old woman, scheduled for total knee replacement, complained of nausea and abdominal pain 30 min after pre-medication with intramuscular atropine and hydroxyzine. Hypoxemia and skin eruption all over her body was noticed in the operating room. Although hemodynamic changes were not observed, the operation was postponed. LST (lymphocyte stimulation test) showed the positive response with hydroxyzine but negative with atropine and antibiotics. This result suggests that hypersensitivity was caused by hydroxyzine in this patient.