Methaemoglobin in man living at high altitude.

Methaemoglobin has been found in the red cells of subjects living permanently at high altitudes (above 3500 m). The level of methaemoglobin appeared to be inversely related to the red cell count and was much increased in anaemic subjects. The methaemoglobinaemia disappeared when the subjects descended to low altitude. The mechanism of this methaemoglobinaemia is not clear. Its presence appears to be related to the hypoxia of altitude, for toxic factors, enzymopenia and the presence of haemoglobin M were eliminated. The regulation of the oxygen dissociation curve in this condition is discussed.