Amniotic fluid (AF) and maternal serum (MS) chorionic gonadotropin (HCG), placental lactogen (HPL), pregnancy-specific beta 1-glycoprotein (SP1), total estrogens (ET), alpha-fetoprotein (AFP) and prolactin (PRL) were measured by enzyme-immunoassays, in 50 normal (A) and in 37 abnormal (B) pregnancies, from 16th to 40th weeks. A: the proteins HCG, AFP and PRL showed a similar decreasing trend after the 20th week, while HPL and SP1 rose progressively throughout the 2nd trimester, thereafter remaining constant. On the contrary ET showed an increasing pattern until term. Chorionic gonadotropin HPL and SP1 in MS were higher than in AF, while AF values of AFP and PRL were higher than in MS, but the ratio MS/AF of all hormone values increased significantly from the 2nd to the 3rd trimester (p < 0.005-p < 0.000001). Estrogens had about the same concentration in AF and MS during the 2nd trimester, but at term of pregnancy, their AF values were double those of MS. B: in polyhydramnios, elevated AF placental hormones were found, while PRL was very low. In erythroblastosis and diabetes, AFP was very low, but placental hormones, PRL and ET were both high and low. In toxemia, SP1, hCG and PRL were elevated, while HPL and ET were very low. In anencephaly and hydrocephaly with spina bifida, AFP was markedly elevated and ET were very low, but in simple hydrocephalus, very low AFP was found. In chromosomal anomalies very high placental hormones and very low AFP and ET were found.