Acute episodes of erythroblastopenia in children with chronic hemolytic anemias have been recognized for a considerable length of time. In 1981, a small virus with a single strand of DNA, parvovirus B 19, was identified as the causative agent in most such episodes. Other diseases have been ascribed to parvovirus B 19, including erythema infectiosum or fifth disease, polyarthralgia, fetal death. Schonlein-Henoch disease, and bone marrow aplasia. In acute attacks of erythroblastopenia, anemia is the most prominent manifestation, but coexistence of neutropenia and thrombopenia has been reported. Hematologic disorders last for approximately ten days. The diagnosis of recent parvovirus B 19 infection rests on detection of specific IgM antibodies, or direct visualisation of the virus by electron microscopy. More recently, detection of the viral genome using molecular hybridization techniques has been achieved. In vitro studies have confirmed the inhibiting effect of parvovirus B 19 on red cell line progenitors, particularly CFU-E, but the exact mechanism of the inhibition remains uncertain. Other diseases due to parvovirus B 19 or other parvoviruses probably remain to be discovered.