Polyarthropathy associated with human parvovirus B19 (B19) is usually transient, but often resembles rheumatoid arthritis (RA).1-3 However, B19 DNA screened by polymerase chain reaction (PCR) may be positive not only in autoimmune diseases, but also in non-arthropathy.4 To study whether or not RA occurs after acute B19 infection, we conducted a prospective study of patients with acute onset polyarthritis. Sixty seven cases showing acute inflammatory polyarthritis from January 1990 to June 1990 were examined and followed up for six years. Among them, 12 (9 female and 3 male) exhibited IgM anti-B19 antibodies.5 PCR, followed by a Southern blot analysis6 also showed the presence of B19 DNA in all 12 cases with IgM anti-B19 antibodies, but did not in the remainder. Initially, rheumatoid factor (RF) was negative in all B19 positive cases except one, but became positive in four, two to four months after the infection (table 1). Among RF …