To the Editor: The alpha-fetoprotein assay is a useful tool in the antenatal detection of neural-tube defects.1 Several other nonspecific abnormalities, including Turner's syndrome,2 omphalocele,3 esophageal atresia,4 congenital nephrotic syndrome,5 duodenal atresia6 and fetal death,7 have been associated with elevated alpha-fetoprotein levels in the amniotic fluid. Abnormal levels may also be caused by contamination of amniotic fluid by fetal blood. In the following case elevated amniotic-fluid alpha fetoprotein was associated with a fetal bladder-neck obstruction due to a posterior mucosal fold. A 37-year-old gravida 2, para 1, was referred for prenatal chromosome studies because of age. An amniocentesis at 16. © 1977, Massachusetts Medical Society. All rights reserved.