The three of us, working in different institutions but in the same city, were very aware of the differences between our diverse approaches to the biology of aging and our perceptions of the sub ject matter. However, three years ago we began to hold informal meetings to discuss our research. These meetings eventually be came more frequent and, with this association, we became increas ingly cognizant of the commonality of our research problems de spite our separate perspectives. The idea for this symposium, therefore, grew from our aware ness that the underlying problem of the biological basis for aging was a common denominator in our research. The papers presented here represent three areas of active investigation: cell divi sion, biological membranes and hormonal regulation. They are sub mitted with the expectations that a greater understanding of the role of each of these separate approaches will help clarify, not only the interrelationships between our fields of research, but more importantly, the biology of aging itself. ACKNOWLEDGEMENTS We would like to extend our sincere thanks for the interest and contributions of the companies listed below: Abbott Laboratories Hoffman-LaRoche Arthur D. Little McNeil Laboratories Bristol Laboratories Mead Johnson & Company Burroughs H'ellcome Co. Merck Sharp & Dohme Research Labs. Charles River Breeding Labs. Rom-Amer Pharmaceuticals Dow Chemical Co. Sandoz Pharmaceuticals E.R. Squibb & Sons, Inc. Schering Corp. Eli Lilly Research Laboratories Smith Kline Corp.