Recruitment into public health intervention trials can be costly and time-consuming. We examined two components of recruitment for an exercise trial: (a) a randomized pilot study of mailing strategies; and (b) the results from the entire recruitment process. In the pilot study, 4,999 women were randomized into one of four groups using a factorial design. The first factor was the inclusion or exclusion of a personal invitation letter, and the second was the use of first-class stamps versus bulk mail. We received 580 (11.6%) responses. Responses from interested women were nonsignificantly higher (odds ratio, 1.19; P = 0.10) for first-class versus bulk-rate postage. However, the cost to randomize one participant using first-class mail was $56.14 (in 1998 dollars) more than for bulk mail. We found no difference in response when including the invitation letter (odds ratio, 1.00; P > 0.50). The general recruitment process identified potentially eligible women primarily through mass mailings but also through media and other sources. We mailed recruitment materials, via bulk mail and including an invitation letter, to 103,577 women in the Seattle area over 2 years. Response rates were different (P < 0.001) between age groups: 6.2% for 50-59-year-old women; 7.9% for 60-69-year-old women; and 7.4% for 70-75-year-old women. The proportion of respondents eventually randomized did not differ by recruitment strategy (mail, media, other). Our study indicates that bulk mail may be more cost-effective than first-class mail for recruitment into intervention trials and that older women are willing to participate in such studies.