Pure red cell aplasia in a lung-transplant patient under immunosuppressive treatment. Bone marrow aspiration shows giant megaloblastic proerythroblasts containing nuclear inclusion bodies and vacuolization of the cytoplasm with absence of other erythroid precursors. Parvovirus B19 genome was found by polymerase chain reaction analysis of the bone marrow and peripheral blood. (Courtesy of Ph. Beris, MD, and K. Samii, MD, Division d'Hématologie, Hôpitaux Universitaires de Genève, Geneva 14, Switzerland.)