The white blood cells (WBC) of peripheral blood are usually the most convenient source of human genomic DNA for DNA analysis with respect to haemoglobinopathies. It is estimated that 10ml of whole blood yield approximately 250μg of DNA, more than sufficient for complete analysis of globin genes with the methods that are currently available (ie based on PCR). DNA is an extremely stable molecule, but enzymes which catalyse the breakdown of nucleic acids (nucleases) are found in all cells. In intact cells the DNA is found in the nucleus and thus is protected from the action of nucleases which are abundant in the lysosomes in the cytoplasm. However when cells are lysed, the membranes of the cell compartments are disrupted, allowing nucleases to come in to contact with the DNA. Thus the first stages of DNA extraction uses buffers which contain inhibitors of nuclease activity. Additionally all steps must be carried out at low temperatures (0^oC). For long-term storage of samples prior to extraction a temperature of -70^oC is recommended. There are many different methods described for DNA extraction from whole blood; the methods described below of salting–out and phenyl chloroform are used in the laboratories of some of the authors. There are also kits on the market for extracting DNA from blood samples which work well, but tend be expensive if used to prepare DNA from 5-10ml blood samples.