From 1st March, 1980 and up to 29th February 1984 a multicenter serum alpha-fetoprotein (S-AFP) screening project was carried out for the detection of severe fetal malformations. S-AFP was determined by a radio-immunoassay in 28 062 pregnant women between the 16th and 20th week of gestation. Patients with elevated S-AFP values, e.g. above 95 percentile, were examined further with a second S-AFP and by ultrasound scan. 244 amniocenteses (0.9%) were carried out to detect 62 malformations (21 anencephalies, 14 spina bifidas, 2 encephaloceles, 7 omphaloceles, 5 gastroschises, 4 chromosome abnormalities and 9 other malformations). Fifteen of the 16 cases of spina bifida could not be verified by ultrasound scan, whereas all other malformations except chromosome abnormalities were confirmed by ultrasonography. Two cases of spina bifida and one case of skin-covered encephalocele had normal S-AFP concentrations and were therefore not detected. There were no definitive false-positives, e.g. therapeutic abortion of a normal fetus. Our conclusion is that a nationwide S-AFP screening should be recommended.