Recent reports have documented human parvovirus B19 infection in pregnancy, which may lead to spontaneous abortion, stillbirth or hydrops fetalis. Transplacental infection in a case of hydrops fetalis is demonstrated by light and electron microscopy observation of virus inclusions in all tissues examined. Parvovirus particles measuring approximately 20 nm were observed within the nuclei of erythropoietic cells. The parvovirus virions were observed most commonly as randomly distributed particles and rarely in crystalline assays. Thus definitive evidence of fetal infection confined to red cell precursors is documented.