The methods used in 1990 and 1991 to trace 998 participants of the Women's Health Study (WHS) who were enrolled during the 1930s in the Menstruation and Reproductive History (MRH) study were described. Some of those enrolled in the study have been lost to follow up for almost 50 years. One of the main tasks of the WHS was to find current addresses for all eligible participants and administer a mailed questionnaire. Specific strategies used by WHS included a review of MRH/Tremin research program files, alumni associations, and yearbook and sorority lists. State level search strategies involved a review of drivers license records, marriage license records, and telephone directories. Search strategies on the national level included health care financing administration, post office records, and credit bureaus. Efforts to identify deceased participants involved reviews of Social Security records, the National Death Index computer file, and death certificates. The advantages and disadvantages involved with each method were discussed. Of the 998 participants, 95% were successfully traced; 170 were confirmed deaths and 773 were found alive. Fifty five participants were not found. Over 160 proxy respondents were identified who completed the current questionnaires. The authors suggest that investigators who study the next several waves of older cohorts may find that they may have greater success in that the study subjects are more likely to have accurate Social Security Numbers available for tracing purposes. Recommendations for others attempting to locate lost members of a longstanding cohort include exploiting unique tracing information about the cohort, begin the tracing with cost effective strategies as well as those that may require processing time, and implement tracing strategies early in the study that are free of charge.