It is my pleasure to introduce the final session of our meeting on cell substrates. So far at this meeting we have discussed the requirements for cells as substrates and the philosophy regarding choice of primary versus continuous cell lines. In addition, we have discussed the use of such cells in the production of newer, live viral vaccines and future needs in regard to the development of new inactivated vaccines and biologicals such as interferon and urokinase. It seems likely that molecular biology will provide us with effective tools to slay the DNA “dragon” which Dr. Hilleman correctly points out represents the genetically dangerous principle in cell lines. In my view, however, it is still somewhat in the future for recombinant DNA to provide large quantities of biologically important molecules for human medicine. Actually the real question with any new (or old) approach is the risk-benefit issue or, to paraphrase an idea of many years ago, “Do the ends justify the means?” Drs. Dull and Cook in this session will provide us with information about the public and its perceptions and needs for involvement in these issues today, as well as the difficult but very important ethical issues surrounding vaccine development and research. Although the subject matter of this meeting has ranged widely, those who have convened it must be congratulated in that their goal of examining critical issues in a significant area of public health medicine for a scientific consensus has been met. All of us will leave this meeting with a deeper understanding of the issues in regard to new vaccine development and with a greater awareness of each other’s positions.