Three patients with erythroblastic hypoplasia were observed for prolonged periods. In one patient, the phenomenon recurred on three occasions over a 12-year period. In the second, erythroblastic hypoplasia accompanied acute hemolytic anemia of the autoimmune type. The third patient had congenital erythroblastic hypoplasia which was observed for 14 years without remission. From the prolonged periods of observation of these three patients, it is concluded that the phenomenon of erythroblastic hypoplasia may develop abruptly, persist for variable periods of time, remit spontaneously and recur unpredictably. A total of four remissions observed in two patients were believed to be spontaneous and not a result of any of the forms of treatment administered. No remission has occurred in a 14-year-old boy with congenital erythroblastic hypoplasia. A classification of erythroblastic hypoplasia is proposed, based on the clinical circumstances in which the phenomenon has been encountered.