Infection resulting in transient reticulocytopenia and anemia, the so called "aplastic crisis," has frequently been documented in patients with congenital hemolytic anemia. However, this association with hematologically normal patients has been less well recognized. Its occasional severity is illustrated by this report of two cases of marked reticulocytopenic anemia in association with probable viral infections. These were previously health children whose anemias could be explained only by a temporary interruption of erythropoiesis. These patients recovered spontaneously and were in good health one year later. A subsequent separate survey of leukopenic patients with a wide variety of viral infections demonstrated significant reticulocytopenia in seven of 35 patient (20 percent). It is concluded that in addition to the more widely appreciated neutropenia and thrombocytopenia of viral infections, reticulocytopenia is a common manifestation of many viral infections and may occasionally result in profound anemia.