This paper investigates the utility of various procedures used to locate and interview veterans as part of a longitudinal research study being conducted for the Department of Defense. The populations are comprised of below entry aptitude standards males who entered the military during the late 1960s, and potentially ineligibles who entered between 1976 and 1980. The latter group entered because of the misnorming of the enlistment exam scores. Several methods was used to locate subjects of both populations and compared to existing data collected from National Longitudinal Surveys on equivalent samples of low-aptitude non-veteran males. Future researchers are encouraged to investigate multiple locating methodologies and assess the quality of existing data and known characteristics of the population prior to embarking on longitudinal data collection with special populations. (Author/SLD)