By the 1960s the dust was settling after a period of great excitement in the biological sciences. It was already established that DNA is a self replicating double helix and that the hereditary message of genes is contained in triplets of n?cleo tides. It was also known that DNA acts as a template the production of messenger RNA, which is transported from the nucleus to the cytoplasm to act as a blueprint protein synthesis, and that amino acids are brought to the messenger RNA template on transfer RNA molecules. And a picture was emerging of how ribosomes interact with these different types of RNA to put together a peptide chain. But these remarkable discoveries had little impact on the clinical world, which found it easier to accept the conclusions of authors such as MacFarlane Burnet, who in his book Dreams, Genes, and Realities wrote: I cannot avoid the conclusion that we have reached the stage in 1971 when little further advance can be expected from laboratory science in the handling of the intrinsic types of disability and disease.1 In the 15 years since Burnet and others wrote off the usefulness of the basic biological sciences there has been a second revolution in biology, which, though perhaps more technical than conceptual, has completely changed the picture. Methods have been developed cutting up genes, cloning them in bacterial cells, and isolating them in bulk structural or functional analysis. In a remarkably short time the stage has been reached when almost any gene worth studying can be isolated and its fine structure determined. But the medical sciences have again been slow off the mark, particularly in Britain. As recently as 1984 Peter Newmark wrote in an editorial Nature: for too many years those that felt obliged to respond to the taunt that molecular biology, all the medical research money it had soaked up, had never done anything to help diagnostic medicine, could, at best, fall back on the case of the thalassaemias.2 Indeed, it is only in the past year or two that clinical scientists have started to see the extraordinary potential of what molecular biology has on offer. Since, as pointed out by Newmark, the haemoglobin disorders, particularly the thalassaemias, have played such a central part in taking molecular biology to the bedside, it will repay a brief examination of how this branch of research has developed and of the subtle interaction between the basic and clinical sciences which has allowed us to reach the stage at which recombinant DNA tech? nology can be applied directly in medical practice.