The rate of globin chain production has been studied in patients with homozygous β‐thalassaemia, heterozygous β‐thalassaemia, haemoglobin E‐thalassaemia, and sickle‐cell‐thalassaemia, and compared with that in non‐thalassaemic individuals. A partial or total deficit of β‐chain synthesis has been demonstrated in all forms of β‐thalassaemia. This results in the production of a large intracellular pool of α‐chains, the kinetics of which have been worked out. The α‐chains in this pool appear to contain haem and are unstable, rapidly becoming associated with the stromal fraction. These findings are examined in terms of the pathogenesis of the anaemia of thalassaemia.