Consecutive serum samples from 5402 women were analyzed for specific IgG and IgM Toxoplasma gondii antibodies by enzyme immunosorbent assay. The prevalence of IgG antibodies was 27.4%. The seroconversion rate was estimated to be 1.16% per year (SE = 0.0017) in all age groups, consistent with an incidence of acute toxoplasmosis in pregnant women of 0.65%. Based on theses figures, the estimated number of congenitally infected cases are discussed. There was no difference in the prevalence of antibodies in women from rural or urban areas, or from different parts of Denmark.