1. A case of dominantly inherited methemoglobinemia is described.
2. Despite the pattern of autosomal dominant inheritance, the hemoglobin is thus far indistinguishable from methemoglobin A and is considered to be normal rather than one of the subtypes of hemoglobin M.
3. The primary defect is one in which there is a decreased capacity to reduce methemoglobin via the normal glucose dependent pathway.
4. The nature of the specific defect remains to be more completely elucidated but is considered not to result from a deficiency of TPN or DPN methemoglobin reductase.
5. Hereditary methemoglobinemia and hemoglobin M disease are reviewed.