Mothers who since 1970 gave birth to children with anencephaly or spina bifida in Hungary are informed about the recurrence risk, the possibility of prevention and about the four institutes where alpha-feto-protein determination is done. In one of these institutes the examination was recommended to 175 women of whom 158 availed themselves of the opportunity. The outcome of their pregnancy is now known in 131 cases. Of these, in 101 the examination was performed because of previous occurrence of anencephaly-spina bifida. High concentration (400, 200, 140 micrograms/ml) were found in 3 cases; they were due to anencephaly (selective induced abortion), severe spina bifida (liveborn) and macerated fetal death. The examination yielded values above the 99% confidence limit in the given gestational week in further 9 cases. The elevated values were due to twinning in 2 cases, to closed spina bifida in 1, and to fetal death in 1 case. The slightly elevated alpha-fetoprotein in 4 of them may have been due to chance.