To increase the use of mammography among women 40 years of age and older, the American Cancer Society (ACS) designed a telephone intervention strategy (the "Tell A Friend" program) that relied on ACS volunteers. During a half-day training session, each volunteer provided a list of 10 women she was willing to contact over a 6-month period and encourage to have a mammogram. Each list was randomized, and five names were returned to each volunteer for inclusion in the intervention. The other women served as controls and were not contacted by the volunteers. All women were subsequently interviewed at the end of the intervention period. Forty-nine percent of the women in the intervention group (n = 289) had received their most recent mammogram since the start of the intervention period, whereas 34% of control women (n = 305) received mammograms during the same time period (p < or = .001, rate ratio = 1.4, 95% confidence interval = 1.2, 1.7). The effectiveness of the intervention remained after controlling for demographic characteristics. The strategy was effective for both black and white women of all ages, but principally among women with annual household incomes of less than $40,000. We conclude that a telephone intervention strategy of personal contacts between acquainted women can significantly increase mammography use, particularly among women with low-to-moderate income.