Sulphemoglobinemia is a condition in which the abnormal pigment sulphemoglobin is found in the red blood cells. The pigment is a combination of sulphur and hemoglobin and is formed in the circulation only under abnormal conditions. The disease is characterized by a cyanosis which may reach any degree of severity and yet is unaccompanied, except in the rarest cases, by respiratory distress. The condition is reputed to be of great rarity. In the whole literature there are not more than thirty cases described; the literature of this country contains only five cases; and it was recently said of Mackenzie Wallis, who had collected five cases himself, that he had seen more than any single observer. Yet in this clinic we have observed eight cases in half a year, and altogether ten in three years—a number that triples the total for the American literature, bringing it up to fifteen cases. THE