Primary infection with Toxoplasma gondii during pregnancy may affect the fetus and result in congenital toxoplasmosis. In Austria serological screening for detection of newly acquired infection during pregnancy was introduced in 1975. In this study we used polymerase chain reaction (PCR) for detection of fetal infection with Toxoplasma gondii. Amniotic fluid samples were analyzed from 11 women with serological indication of acute toxoplasmosis infection. Nine of these women had already received treatment prior to amnio-centesis and no evidence of Toxoplasma gondii DNA was detected with PCR in the respective amniotic fluid samples. Isolation of the organism by mouse inoculation was negative in these cases and follow-up serology as well as clinical examination of the infants confirmed these results. In 2 patients investigation of the amniotic fluid samples by means of PCR was positive; both women had not yet been treated at the time of amniocentesis. Our results indicate that identification of Toxoplasma gondii in amniotic fluid is a useful procedure for diagnosing or excluding fetal infection. Moreover, the current recommendations of the screening program appear to be successful in preventing congenital toxoplasmosis.