To the Editor.— The recent article by Dr Schilling 1 suggests that the administration of oxide to patients with subclinical vitamin B 12 deficiency may produce neurological and hematological deficits. However, several details relating to the patients' history and anesthetic management are omitted in the article and could alter the author's conclusions. Moreover, readers not familiar with the specialty of anesthesiology may be confused by certain expressions in this manuscript, and these areas need to be clarified. First, throughout the manuscript Dr Schilling uses the phrase nitrous oxide anesthesia. In fact, oxide alone will not produce a state of anesthesia unless it is administered at hyperbaric pressures. 2 In the clinical setting, oxide is always administered in combination with oxygen and almost always with other inhaled or intravenous anesthetics. The additional anesthetic agents employed in the two cases described by Dr Schilling are not specified. In case