The development of molecular medicine will be illustrated by several approaches to the diagnosis and possible gene therapy of some haematological and malignant disorders. Firstly, the history of the prenatal diagnosis of the hereditary blood disease thalassaemia will be traced from bloof test to DNA test. New developments that may allow a foetal diagnosis to be made from a blood sample taken from the mother will then be presented. Finally, various approaches for gene therapy will be reviewed and, as examples, experimental approaches in treating hepatoma will be outlined.