Alpha-fetoprotein was determined by electroimmunodifiusion and radioimmunoassy in 109 neonatal urine samples and 94 amniotic fluid samples. The samples were obtained from newborns and from pregnancies ranging in gestational age from 20 to 40 weeks. When α-fetoprotein values of neonatal urine and amniotic fluid were correspondingly correlated with gestational age, almost identical declining curves could be drawn. Twenty-one cerebrospinal fluid samples from newborns ranging from 25 to 40 weeks of gestation were similarly determined. No correlation between cerebrospinal fluid α-fetoprotein and gestational age could be demonstrated. It is concluded that fetal urine is the major source of α-fetoprotein in the amniotic fluid of normal pregnancy. In pregnancies associated with neural tube defects, α-fetoprotein elevation is probably not due to the leakage of cerebrospinal fluid into the amniotic cavity.
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