Abstract
1. Tritiated histidine and leucine are incorporated into hemoglobin by rat and dog reticulocytes and fulfill the conditions of a good red cell label for autoradiographic studies.
2. After mild erythropoietic stimulation, all reticulocytes appear to mature into normal red cells with expected lifespans.
3. After marked erythropoietic stimulation, the reticulocytes mature into red cells with normal potential lifespans but decreased mean lifespans.
4. In one animal studied, macrocytes produced by increased erythropoietic stimulation were found to have the same magnitude of shrinkage as do normal red cells.
5. The normal maturation time of the rat reticulocyte in the blood is about 33 hours in vivo and is increased following erythropoietic stimulation.
