Parvovirus B19 is the causative agent of erythema infectiosum. In addition, the infection may be associated with other disease manifestations: anemia and aplastic crisis, thrombo- or granulocytopenies; spontaneous abortion or hydrops fetalis in pregnant women; acute and chronic arthritis in adults and children, myocarditis and hepatitis. Both acute and persistent courses of B19-infections have been reported. All patients develop IgG against the capsid proteins VP1 and VP2, the majority of virus neutralizing antibodies that offer life-long protection against reinfections are directed against the VP1-unique region. IgM is mainly directed against VP2-specific epitopes. These antibodies may be present for only a rather short period of two to ten weeks after acute infection. IgG-antibodies against the nonstructural protein NS1 are preferentially found in patients which are unable to eliminate the virus and develop persisting viremia or virus persistence in distinct organs, e.g. synovial fluid, liver, bone marrow.