Performing prenatal diagnosis of congenital developmental abnormalities, the authors have studied two biochemical parameters in maternal serum: alpha-1-fetoprotein (MS AFP) and trophoblast-specific beta-1-glycoprotein (MS SP1). MS-AFP and MS-SP1 examinations were performed between the 15th and 20th week of pregnancy as a screening of all pregnant women in Benesov district (n = 3150), all risk pregnancy patients of the faculty hospitals of the First Medical Faculty, and patients of the Department of Medical Genetics (First Medical Faculty). The group studied also includes five retrospectively traced patients in the third trimester of pregnancy who had delivered fetuses with chromosomal aberations. Sevatest ELISA AFP Micro I kit (USOL) was used to assess MS AFP. The results were computerized using KIM programme (USOL). MS SP1 was assessed by simple radial immunodiffusion with the use of Q antiserum SwAHu/SP1 and standard serum (USOL). During prenatal screening of women in the second trimester of pregnancy 6 morbus Down fetuses have been detected. In three of these patients the levels of MS AFP were lower or equal to 0.5 multiples of the median (MOM), in three women MS SP1 levels were higher than 1.9 MOM MS SP1, both pathological parameters having been found in two patients. In pregnancies with Edwards syndrome fetuses MS AFP levels were physiological or slightly elevated. MS SP1 levels being 1.6 and 1.9 MOM respectively. In patients in the third trimester of pregnancy the MS SP1 values were 1.1 to 2.1 MOM. In the patient with Edwards syndrome fetus MS SP1 levels were repeatedly found to be physiological.(ABSTRACT TRUNCATED AT 250 WORDS)