Human gene therapy continues to be an exciting concept for the treatment of disease. This field of research remains in its early stages, but already a number of studies have provided "proof-of-principle." Although there is no unequivocal evidence of efficacy, there have been demonstrated physiologic changes that are relevant to the disease process. One of the major challenges still confronting the field is the design of more efficient vectors. The gene delivery systems being used today will undoubtedly be seen as crude when compared with future developments. It is unlikely that there will ever be a universal vector, but rather there will be multiple vectors specifically designed for certain organ sites and certain disease. It is reasonable to assume that, in the future, there will be synthetic vectors that co-opt the needed properties from both cells and viruses. It will be necessary to do much more fundamental research in cell biology, virology, immunology, and pathophysiology before vectors can be significantly improved. Many of the tools for this research are in place, and the driving force will be provided by the imaginativeness of the committed investigators.