Most longitudinal studies are designed to serve fairly narrow purposes, such as the prediction of life outcomes from theoretically relevant antecedent variables, or the documentation of age-related changes in the level of personality or cognitive variables. However, the accumulation of data on a single group of people observed over a period of many years permits a variety of other types of analyses. Creative use of a longitudinal archive can amply justify the costs of maintaining the sample and should encourage investigators to initiate more longitudinal projects. Findings from the Baltimore Longitudinal Study of Aging are used to illustrate both traditional and alternative uses of personality data, including (a) development of nomological nets for the interpretation of personality measures, (b) evaluation of state effects in personality measurement, (c) validation of retrospective reports, and (d) heuristic exploratory analyses. Current knowledge on the stability of personality in adulthood, the correspondence of observer ratings and self-reports, and the comprehensiveness of the five-factor model can enhance the design of future longitudinal studies.