The mechanisms for cellular aging have yet to be elucidated, but most data are in favor of a combination of processes. Such theories include a neuroendocrine group of theories, an immunological theory, the theory with a limited number of cell divisions as a basis, and the "wear-and-tear" theories together with e.g. oxidative stress and DNA damage. New data on cardiac aging have implications for geriatric medicine. With advancing age, although body cell mass decreases, the amount of body fat is relatively unchanged, while a more marked change from age 70 entails a reduction in body water. Data on successful attempts to prolong life in man are scarce, even if life-span in animals has been manipulated.