1. Comparative studies of reticulocyte percentages have been made on the spleens of normal dogs, dogs with phenylhydrazine hemolytic disease, and human cases of hemolytic jaundice. Splenic artery and vein blood has been compared in some of these, both before and after adrenalin.
2. No significant differences were found, as between peripheral, splenic arterial and venous blood, with or without the use of adrenalin.
3. Imprint and "squeeze" preparations of splenic parenchyma consistently gave higher percentages ranging from 1.5 to 3.5 times the peripheral values, the most marked differences being noted in the normal dog (11.5 to 27 x).
4. The possible significance of these findings is discussed.