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.

Inhalt
Regulation of Cell Division in Aging Mouse Mammary Epithelium.- Age Dependent Decline in Proliferation of Lymphocytes.- The Regulation of Cellular Aging by Nuclear Events in Cultured Normal Human Fibroblasts (WI-38).- Hydrocortisone as a Modulator of Cell Division and Population Life Span.- General Considerations of Membranes.- Function of Cardiac Muscle in Aging Rat.- Changes in Cardiac Membranes as a Function of Age with Particular Emphasis on Reactivity to Drugs.- Changes in Protein Synthesis in Heart.- Senescence and Vascular Disease.- Changes in Hormone Binding and Responsiveness in Target Cells and Tissues During Aging.- Regulation of Corticosterone Levels and Liver Enzyme Activity in Aging Rats.- Aging and the Regulation of Hormones: A View in October 1974.- Aging and the Disposition of Glucose.- Banquet Address.- The Scientist and Social Policy on Aging.- Abstracts.- Cell Types Originating from Young and Old Mouse Kidney Explants.- Alterations in the Growth Rate and Glucose Metabolism of Chinese Hamster Cells inVitro.- The Cristofalo Indices of Mutant Human Cells.- Altered DNA Metabolism and Aged and Progeric Fibroblasts.- The Survival of Haploid and Diploid Vertebrate Cells After Treatment with Mutagens.- Capacity of Cultured Fibroblasts from Different Mammalian Species to Metabolize 7,12- Dimethylbenz(a)anthracene to Mutagenic Metabolites: A Correlation with Lifespan.- Extension of the inVitro Lifespan of Human WI-38 Cells in Culture by Vitamin E.- Diminished Inotropic Response to Catecholamines in the Aged Myocardium.- Studies in Age-Related Ion Metabolism in Rat Myocardium.- The Effects of Isoproterenol Stress on the Hearts of Old and Young Rats.- The Effect of Age and Fasting on Serum Cholesterol Levels and Cholesterol Esterification in the Rat.- Lipid Metabolism in Aging Rats.- Exercise, Thyroid Secretion Rate and Lipid Metabolism in Rats.- Accelerated Aging of the Brain: Neuroendocrine Studies in Huntingdon's Disease.- Changes in Brain Adenosine 3'5' Monophosphate in the Aging Rat.- Evidence Relating the Amount of Albumin mRNA to the Increased Albumin Synthetic Activity Observed in Old Rats.- Properties of Catalase Molecules in Rats of Different Ages.- Thermal Denaturation of Biomolecules at Normal Body Temperature.- Participants.