Pregnancy-specific beta 1-glycoprotein (PSBG) levels in amniotic fluid were studied by radioimmunoassay in 70 normal and 90 high risk pregnancies between 34 and 41 weeks. Most values from high risk singleton pregnancies were within the normal range. Intra-uterine growth retardation (n = 22) was associated with normal amniotic fluid PSBG levels. In twin pregnancies, the amniotic fluid PSBG values were usually above the normal mean, but within the normal range. The average ratio between amniotic fluid and maternal serum PSBG concentrations was 1:16. Amniotic fluid PSBG concentration did not correlate with the maternal serum PSBG level, and no relationship with fetal distress, infant birth weight or length, sex or placental weight was observed.