Using the new DNA technology, it is now possible to offer prenatal diagnosis or presymptomatic testing for many genetic diseases. For prenatal diagnosis, foetal tissue is obtained y chorionic villus sampling at 9 to 11 weeks gestation or amniocentesis at 18 weeks. The programme in Hong Kong, which started in 1982, is reviewed here and now included alpha and beta thalassaemia, haemophilia A and B, Duchenne muscular dystrophy, Huntington's diseases, and spinal muscular atrophy. DNA diagnosis can now be performed using a single cell obtained from pre-implantation embryos or from rare foetal cells isolated from maternal peripheral blood. The latter is safer and more acceptable to parents. Presymptomatic testing for untreatable diseases such as Hungtington's disease poses new ethical and social problems that need to be resolved. As many more genes are being discovered, prenatal diagnosis and presymptomatic testing programmes will continue to meet new challenges in the future.