Approximately 100 human fibroblast-like cell lines derived from the upper arms of members of the Baltimore Longitudinal Study have been deposited in the Aging Cell Bank at the Institute for Medical Research, Camden, N.J. These cell lines were derived from individuals ranging from 29 to 96 years in age. The in vitro lifespan of each culture has been estimated by the distribution of colony sizes. The availability of cell lines of known proliferative potential from donors of various ages should provide an important new resource for cellular aging studies.