A case is reported in which a patient developed cyanosis under general anesthesia due to methemoglobinemia. The cause of the methemoglobinemia was benzocaine applied topically to the pharynx and trachea. When confronted with cyanosis in the absence of cardiac or pulmonary disease, one must seriously consider the diagnosis of methemoglobinemia. Supplemental oxygen should be administered and methylene blue given intravenously. If possible, determination of arterial blood gases should be made to obtain the methemoglobin concentration. Finally, all medical and dental personnel using benzocaine should be aware of the recommended dose and the possible complications of overdosage.