In 1987, the Division of Cancer Prevention and Control, National Cancer Institute (NCI), funded a randomized trial of a proactive counseling protocol to promote screening mammography among age-eligible female callers to the Cancer Information Service (CIS). This protocol included interactive counseling by CIS counselors to help callers overcome barriers to screening mammography; this counseling was an extension of usual service and was combined with a 2-week follow-up mailout to reinforce the brief (6-minute) proactive telephone-counseling protocol. The screening-mammography counseling intervention was tested in two regional CIS offices using a randomized two-group design. Callers were randomly assigned to the intervention or control group based on the week of their call to the CIS (n = 1831 eligible female callers). Self-reported adherence to NCI screening-mammography guidelines was assessed from telephone interviews conducted at 12 months' follow-up (87% response rate). Among all CIS callers enrolled in this study, self-reported adherence to screening-mammography guidelines at 12 months' follow-up was 63.5%. The most frequently cited barriers to screening mammography reported by CIS callers were inconvenience/being too busy (52%), cost (36%), lack of physician referral (34%), no symptoms (34%), and fear of radiation (29%). A significant intervention effect on adherence behavior was found but only in one of the two test sites and only among CIS callers reporting total family income of $30,000 or more (odds ratio = 1.38, P = .04). The vast majority (90%) of CIS callers (both intervention and control subjects) endorsed the concept of proactive counseling by the CIS. The implications of these findings for the CIS and future research are discussed.