Over a period of 29 months, from January 1991 to December 1994, all cases of acute polyarthritis seen at the Rheumatology Service in our Institution were studied to determine the seroprevalence of parvovirus B19 (B19) infection. The variables studied included: age and sex of patients, presence of fever and rash, Anti-B19 IgM and IgE serological determinations (ELISA, Mardix Lab.), follow-up time and final diagnosis. The study included 36 patients (22 women and 14 men, mean age 34 +/- 19 years). Thirteen and seven patients had fever and cutaneous rash, respectively. Anti-B19 IgM serology was positive in 4 patients; in 2 of them IgG seroconversion was confirmed. The mean follow-up time was 14 +/- 9 months. Final diagnoses included undifferentiated polyarthritis, rheumatoid arthritis, B19 polyarthritis, systemic lupus erythematosus, and miscellaneous in 19, 7, 4, 2, and 4 patients, respectively. Seroprevalence of B19 infection in acute polyarthritis in our area was 11%, approximately.