We analyzed nutrient levels in amniotic fluid obtained during the second trimester of normal, uncomplicated pregnancies from 221 women who delivered apparently healthy infants and from 8 with neural tube defect (NTD) pregnancies. Folate was measured by microbiological assay, vitamin B12 by a radiobinding method, and zinc, copper and iron by atomic absorption spectrophotometry. We found that the mean amniotic fluid nutrient levels of normal pregnancies were 24.7nmol/l for folate, 600pmol/l for vitamin B12. and 1.7. 1.9, and 9.0 µmol/1 for zinc, copper and iron, respectively. Amniotic fluid folate, zinc, copper and iron levels of NTD pregnancies were similar to those found during normal pregnancy. however, vitamin B,2 levels were markedly lower than those of normal pregnancies. © 1992 S. Karger AG, Basel.