A 65-year-old man with a 15-year history of 'leukemicised' low-grade lymphocytic B-cell non-Hodgkin lymphoma with a low-titre of IgM kappa paraprotein was admitted with severe anaemia and reticulocytopenia. Treatment with prednisone and chlorambucil had been started two weeks earlier because of a recently diagnosed Coombs-positive haemolytic anaemia. He also received a blood transfusion at that time. During his stay in the hospital, a crista biopsy was performed that revealed no signs of bone marrow suppression but markedly enlarged pro-erythroblasts. Although a serologic test for Human Parvovirus-B19 was negative, PCR showed a sharply increased viral load with more than 1 x 10(11) copies/ml, compatible with a primary parvovirus infection. In retrospect, an earlier transfusion of blood that had not been screened for parvovirus was probably the culprit. Treatment with human immunoglobulin was effective in lowering the viral load and normalising the haemoglobin. This case illustrates that reticulocytopenia in a patient with a haematologic disorder accompanied by a shortened erythrocyte life-span is suggestive for a primary parvovirus infection, especially following a recent transfusion. To prevent transmission of Human Parvovirus B19 via blood transfusion, the Health Council of the Netherlands published a guideline indicating that patients at high risk for a complicated infection with Human Parvovirus B19 should be given 'virus-free' blood products.