PIP: Maternal serum alpha fetoprotein (AFP) screening is a potentially valuable tool for the in utero detection of fetal neural tube defects. The United Kingdom Collaborative Study of 18,985 pregnancies detected 88% of fetuses with anencephaly and 79% of those with spina bifida through such routine screening. However, the development of a national strategy in the U.S. to submit all pregnancies to AFP screening is being slowed by several problems. Since the normal AFP concentration is different for each gestational week, the precision and sensitivity of the radioimmunoassay must be assured and exact gestational age confirmed by high-quality sonography. In addition to ultrasound, other ancillary services required include cell culture facilities, amniotic fluid AFP assays, and genetic counseling. The detection rate is highest after 18 weeks gestation, leading to time constraints if abortion is elected. Also, many women make their 1st antenatal visit after this point. Still unknown is the frequency of false-positive and false-negative results or the extent of racial variations in serum AFP levels. Since elevated serum AFP levels may also indicate maternal disease, other congenital abnormalities, obstetric complications, or a multiple pregnancy, the screening rather than diagnostic nature of this tool should be emphasized. While rough calculations suggest that the cost to society of the care for neural tube defect patients would be over 10 times that of an effective screening program, cost-benefit analyses are confounded by a lack of knowledge of the degree of patient compliance that can be expected. The greatest cost efficiency, as well as the best care, can be secured through the development of regional centers with all the necessary ancillary services.