During the last few years new powerful diagnostic methods have been developed in the field of molecular and cell biology. It is now possible to work out the molecular pathology of many genetic diseases and to institute new techniques for the detection of carriers and neonatal diagnosis. However, it is in the field of polygenic diseases such as degenerative vascular disease, diabetes, cancer and other chronic diseases that molecular biology will play its most important part and perhaps change in the long term our clinical approach. There is considerable debate among geneticists on the safest strategy for obtaining and long term storing sufficient DNA from an individual for projects requiring large but unknown amounts of DNA. As little as 0.5 ml whole, blood samples (or white cells) which have been frozen with 10% DMSO or anticoagulants will provide sufficient DNA by direct extraction methods and also permit to establish lymphoblastoid cell lines providing an infinite source of DNA.