A method is described of assessing the degree of maturation of erythroblasts in the marrow of adult rabbits. It has advantages over the conventional system of classification into pronormoblasts, basophilic, polychromatic and orthochromatic erythroblasts. Examples are given of the normal and two different extreme pictures: severe anemia (phenylhydrazine) and the early recovery stage after a nearly lethal injection of nitrogen mustard.

A method is described for segregating erythroblasts from adult normal rabbit marrow according to their degree of maturation. The erythroblasts are fractionated by centrifugation is a bovine serum albumin density gradient. A useful adjuvant procedure was prior lysis of the initial marrow cell suspension by an antiserum (goat) to rabbit erythrocytes. The appropriate concerntration of antiserum, with complement, lysed nearly all the acidophilic erythroblasts, reticulocytes and erythrocytes; basophilic erythroblasts remained, fewer, but more immature, the higher the concentration of antiserum used. Erythroblasts of the severely anemic (phenylhydrazine) rabbit were not fractionated as well as those of the normal by the centrifugation and not at all by the immune hemolysis procedure.