Ferrara type of beta 0 thalassaemia has two unusual features: first, normal beta-globin chain synthesis is inducible either in cell-free systems prepared from patients' reticulocytes by adding supernatant factors from non-thalassaemic reticulocyte lysates or in heterologous cell-free translation of thalassaemic mRNA; second, beta-globin synthesis is inducible in patients in vivo after blood transfusion. We now describe a molecular lesion of the beta-globin gene that is common to nine cases of Ferrara beta 0 thalassaemia but cannot be reconciled with the inducible response.