Although thousands of articles and hundreds of books on aging have been published, only a small percentage of this material has dealt with anatomy, particularly at the fine structural level. It was with this in mind that Aging and Cell Structure was conceived. Volume 1 of Aging and Cell Structure was published in 1981 and represented a current compilation of information, concentrating at the electron microscopic level, on morphological changes which occur in cells and tissues as they age. The present volume completes the two-volume set. While Volume 1 highlighted structural changes occurring in the aging nervous system, Volume 2 centers its efforts on studies of in vitro aging. Chapters on other subjects are included as well. These include age-related changes seen in neuromuscular junctions, oral tissues, and the pancreas. Although these two volumes represent a very small part of the published infor mation on experimental gerontology, their approach is rather unique because they focus on anatomy, perhaps the most basic of all the biomedical sciences. Because many dif ferent tissue types are examined, we begin to see recurrent, definitive patterns in the aging cell which may not be fully apparent from studies taking one cell type at a time. This becomes even more evident in the present volume where changes seen in popula tions of cells grown in culture-isolated from hormones or nervous impulses from other body areas-are found to be similar to those changes found in vivo.