Prenatal diagnosis for familial hypercholesterolaemia (FH) was performed by using restriction fragment length polymorphisms (RFLPs) of the LDL receptor gene on chorionic villi DNA taken during the 10th week of pregnancy. Both parents were FH heterozygotes and had previously had a healthy son and an FH homozygous son. Two RFLPs were informative in this family and revealed that the fetus was unaffected by FH. At birth the child was found to have an LDL cholesterol level of 30 mg/dl and a normal LDL receptor activity in cultured umbilical cord fibroblasts. RFLP analysis on chorionic villi DNA is highly recommended for all heterozygous FH couples in whom the LDL receptor gene mutation/s is/are still to be characterized.