Examination of the genetic mechanisms underlying the thalassaemias has led to a clearer understanding of the control of eukaryotic genes in general. Inherited disorders of haemoglobin synthesis are an important cause worldwide of morbidity and mortality, and place a large burden on patients, families, and ultimately communities. The haemoglobin disorders can be controlled, by counselling and prenatal diagnosis. Treatment is usually symptomatic, though bone-marrow transplantation for beta-thalassaemia may be successful in suitable patients.