Antibody prevalence to B19 virus in Japan was previously reported with 1973 and 1984 serum collections. Since then we have had two big epidemics of erythema infectiosum in Japan: 1986-87 and 1991-92. In an attempt to estimate how much those epidemics have affected seroprevalence to B19 virus infection, we studied seroepidemiology in three separate areas using a newly developed ELISA system consisting of recombinant VP1 + VP2 particle antigen. Total of 900 sera obtained in 1993 from healthy individuals living in northern, central and southwest parts of Japan were assayed for the presence of and B19 IgG antibody. In the first, the new assay system was compared with our conventional assay system in which native B19 virus particles were used as antigen. Of 220 serum samples tested, 212 (96.4%) gave same results in both assays. Remaining 8 samples which gave variable results were those of near cut off values. We concluded that this new ELISA system can be recommended for seroepidemiological use. Antibody prevalence rates were 10%(0-4 y), 54%(5-9 y), 59%(10-14 y), 46%(15-19 Y), 38%(20-29 y), 48%(30-39 y), 64%(40-49y) and 76%(50 y-). No gender difference was observed. Comparison of antibody prevalences in 1973, 1984 and 1993 suggested that approximately 10%(about 8 million people) of the total population under 40 years of age acquired immunity to B19 virus during one epidemic period.