DNA samples from 60 Chinese patients with haemoglobin H disease were analysed by restricted endonuclease mapping to determine the patterns of alpha-globin gene organisation and the distribution of these patterns in China. Restriction endonuclease analysis and rapid micro-DNA hybridisation on nitrocellulose membranes were also used to analyse DNA from amniotic fluid cells or from chorionic villi in 7 pregnancies at risk of haemoglobin Barts hydrops fetalis, in 1 at risk of haemoglobin H disease, and 1 at risk of both disorders.