PIP: A method for determining fetal sex by identification of Barr-Body in amniotic fluid by staining with aceto-orcein 120 patients pregnant for 20-40 weeks (Group 1) and 50 patients pregnant for 14-20 weeks (Group 2). The results were confirmed at birth or abortion. The accuracy of fetal sex diagnosis was 98.33% in Group 1 and 100% in Group 2. The method is extremely rapid, requiring no more than 10 minutes to complete the procedure. It is recommended that another method be used to confirm the results of the aceto-orcein staining method if a question of therapeutic abortion is involved.