Abstract 1. 1. Albino and wild rats and the ground squirred ( Citellus tridecemlineatus) were subjected to hypoxic conditions at stimulated altitudes of 20,000 ft. 2. 2. No appreciable difference between albino and wild rats in terms of their weight gain and loss, hemetocrit, hemoglobin or 59-Fe uptake in response to hypoxic stress was noted. 3. 3. Ground squirrels used as an example of a hibernator differ from non-hibernating rodents in that under hypoxic conditions their mortality is less; they do not show as great an increase in percentage rise of hematocrit or hemoglobin but show a greater increase in erythopoietic activity as indicated by 59-Fe uptake. 4. 4. Hibernators appear to have greater capacity to survive under hypoxic conditions.