In 1958 chorionic villus samples, investigated by culture method, we found 137 (7%) abnormalities. The abnormal results were classified in certain abnormal (generalised abnormal at high probability) and uncertain abnormal (potentially confined to the placenta) results. Certain abnormal were 73 cases (3.7%). Uncertain abnormal were 64 cases (3.3%), in which confirmation studies were done in 47 cases. In 12 cases of these 47, the abnormality was confirmed and in 35 cases (1.8%) the abnormality was confined to the placenta. Among the latter cases, poor pregnancy outcome [16% intrauterine death (IUD), 6% intrauterine growth retardation (IUGR)] was increased. Total maternal cell contamination was not seen. The positive predictive value of all confirmed abnormal cases was 66%. The positive predictive value was 100% for indications 'ultrasound abnormalities' and 'carrier' and between 50 and 60% for all other indications. Predictive value among uncertain abnormal cases was low (26%). However, the positive predictive value depends of the type of abnormality. Therefore we conclude that the culture method for chorionic villi is a good test for indications 'ultrasound abnormalities' and 'carrier' and reliable for all other indications. Whether or not follow-up investigations should be offered to the parents depends of the type of abnormality. We conclude that the culture method is reliable for prenatal diagnosis and can be used as the sole investigative method.