Restriction endonuclease analysis of the human beta-globin gene cluster has revealed a new DNA polymorphism at a Pvu II recognition site approximately 3.5 kilobases from the 3' end of the Agamma-globin gene. In patients from the Mediterranean area, the Pvu II polymorphism was associated equally with both normal and beta-thalassaemia chromosomes. In patients of Indian and Pakistani origin the polymorphism was almost exclusively associated with only the normal chromosome. Therefore this site may prove very useful for the antenatal diagnosis of beta-thalassaemia by acting as a genetic marker for the normal chromosome in linkage analysis of family members.