1. The literature concerning attempts to produce macrocytic anemia of the liver-deficiency type in animals by operations on the gastrointestinal tract has been reviewed. Operations on the stomach have failed consistently to produce such an anemia, but success has been achieved by operations on the small intestine with the creation of blind loops or intestinal stenosis.
2. The technic we have used to produce macrocytic anemia in the rat is described in detail. The essentials are that the blind loop should fill with peristalsis and that it should not be too low down in the small intestine.
3. Anemia does not usually develop until an interval of several weeks or months after the operation. It is then macrocytic in type and acute in course.
4. The anemia is probably dependent on stagnation in the blind loop and a change in the bacterial flora of the small intestine.