Unexpected cyanosis in the surgical patient.

Benzocaine is a commonly used topical anesthetic present in many over-the-counter preparations. The development of methemoglobinemia, associated with the use of benzocaine, is potentially fatal. Methemoglobinemia remains unresponsive to the administration of oxygen alone and, in fact, results in greater tissue hypoxemia than the usual monitoring techniques indicate. We report two cases of benzocaine-induced methemoglobinemia occurring 3 months apart at the same institution. A brief discussion regarding methemoglobin is presented.