In seven patients with marked megaloblastic anemia (MCV greater than 110 fl), red cell size distribution curves (erythrograms) demonstrated the size of red cells produced after therapy. In six, the new red cells were normocytic throughout recovery. In the seventh patient, folate repletion along produced a new population of microcytes, due to unsuspected iron deficiency; after iron repletion normocytes were produced. Three patients with autoimmune hemolytic anemia had macrocytosis (MCV greater than 110 fl) without folate or vitamin B12 deficiency. During recovery with predisone therapy, instead of a discrete new normocytic population appearing, the entire population progressively returned to normal size. Normal rather than “stress” reticulocytes, and remodeled stress reticulocytes remaining, may explain this different pattern of recovery. Two patients initially had minor subpopulations of smaller red cells that disappeared soon after therapy. These probably reflected the dyserythropoiesis of severe megaloblastic anemia.