Thirty-six pregnancies in 25 families at risk of beta-thalassaemia major received prenatal diagnosis. Chorionic villus sampling or amniocentesis was done in 35 pregnancies to obtain fetal cells for DNA linkage study, for which Southern blotting and DNA hybridization were used to detect seven restriction fragment length polymorphisms (RFLPs) within the beta-globin gene cluster: epsilon-HincII, G gamma-HindIII, A gamma-HindIII, phi beta-HincII, 3' phi beta-HincII, beta-AvaII, and 3' beta-BamHI. beta-Thalassaemia major was diagnosed in seven and excluded in 22 pregnancies. In the remaining six cases, beta-thalassaemia major could not be excluded. In these six pregnancies and another one with late booking, ultrasound-guided cordocentesis was performed at the 22nd to 27th week of gestation. Globin chain composition was determined with urea-acetic acid-Triton X-100-12 per cent polyacrylamide gel electrophoresis. beta-Thalassaemia major was diagnosed in two fetuses and excluded in the other five. Eleven fetuses (in which beta-thalassaemia major was excluded) have been delivered and are healthy at more than 5 months old. DNA linkage analysis coupled with globin chain electrophoresis provides an effective way for prenatal diagnosis of beta-thalassaemia major, although these methods are being replaced by more direct detection techniques using oligonucleotide probes.