Haemoglobinopathies are inherited conditions characterized by:(i) the synthesis of an abnormal haemoglobin (Hb), or (ii) the failure to synthesize a normal amount of Hb. An understanding of the biochemical and genetic factors which determine the haemoglobinopathies of the second type can only be reached by having a detailed knowledge of Hb synthesis. However, even after the recent dramatic progress in our knowledge of protein synthesis [1], we are far from a full understanding of the control of this biosynthetic process in higher organisms. Complex regulatory mechanisms determine the Hb type synthesized by erythroid cells, the rate of synthesis of globin, and that of haem, and the relative amount of a given Hb in erythrocytes, when more than one Hb type is synthesized. Some of these regulatory mechanisms are clearly determined at the chromosomal level by regulatory genes, which may interact with cytoplasmic repressors or activators [2], whereas other regulatory mechanisms are operating at the translational or cytoplasmic level [3], since they can be observed at work in the anucleated reticulocytes. Little is known of the chromosomal regulatory mechanisms, whereas more information is today available on cytoplasmic regulatory mechanisms, which are more accessible to investigation and can be tested in reticulocytes or in cell-free systems prepared from reticulocytes. Some knowledge of chromosomal regulatory mechanisms can presently be derived from the study of mutations of Hb genes, which change the normal pattern of Hb synthesis [4]. The study of these chromosomal regulatory mechanisms may provide in the long run information essential for the understanding of cellular differentiation and proliferation.