Abstract
Prenatal diagnosis of Tay‐Sachs disease was performed using the sulphated substrate 4‐ methylumbelliferyl‐6‐sulpho‐2‐acetamido‐2‐deoxy‐β‐D‐glucopyranoside to detect hexosaminidase A in chorionic villi. The presence or absence of hexosaminidase A in villi was detected by both a quantitative enzyme assay, and by a rapid, novel procedure which permitted visual discrimination between normal and affected villi.