Among 1600 pregnancies, in which amniocentesis for prenatal diagnosis had been performed, were 73 cases with previous threatened abortion. In none of these abortion occurred after amniocentesis. 56 children have been born so far. There is evidence for a slight but not statistically significant increase in the number of multifactoral anomalies in this group. This study supports former findings of a higher prematurity incidence after vaginal bleeding in early pregnancy. If amniocentesis took place after imminent abortion, brownish discoloured amniotic fluid has been withdrawn in 53%. This phenomenon probably results from transfer of blood substances from hematomata between uterine wall and amniotic sac. Cultivation of amniotic fluid cells may be impaired by those degradation products, prolonging the cultivation period for an average of 2 days. Special methodological modifications to enhance the success of amniotic fluid cell cultivation in those heavily contaminated specimens are discussed. There seems to be no interference with AFP-estimation. Fetoscopy vision may be impaired.