Knowledge of the pathophysiological mechanisms governing Parvovirus B19 infection has been modified with the recent discovery of its cellular receptor. The cell lines susceptible to infection can be identified on the basis of the nature and distribution of the virus in the human organism. The Parvovirus B19 can undergo two types of cycles within the host cell. The first is a complete cycle within the infected cell leading to cell death by lysis. In the second, the cycle aborts and cell death is caused by an association of immunological phenomena and the accumulation of viral proteins toxic to the cell. It is not known why complete cycles are restricted to a single erythrocyte line. These new data not only give a more precise explanation of the classical clinical expression of the disease, but also suggest possible mechanisms for the pathogenic power of the Parvovirus B19, some of which have already been proposed on the basis of clinical observations.