In normal rats serum B12 activity was found to be similar to man but serum folate activity was a good deal higher, in the range of 129 mµg./ml. Total body radiation and administration of 3MCA did not significantly alter B12 or folate activity. Osborne-Mendel rats maintained on a vitamin A-deficient diet were found to have markedly lowered serum B12 activity; the folate levels were only slightly decreased.

Studies on leukemic rats showed that eight animals with myelogenous leukemia had no elevation of the serum B12 activity, and in these animals folate levels were slightly reduced. In two rats with radiation-induced acute lymphatic leukemia, serum B12 activity was significantly elevated due to hepatic necrosis, and folate values were somewhat below normal levels.

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