Background. In this paper two large nationwide trials are described, both of which will test a comparable telephone-based counseling intervention to promote cancer screening among the first-degree relatives (FDRs) of breast and colorectal cancer patients. The unit of randomization will be the family unit of eligible FDRs. Access to FDRs will be obtained from their relatives with cancer. Selected intervention and design issues are reviewed, including how both projects will respond to FDRs who exhibit significant levels of cancer-specific anxiety or distress and how potential high-risk cancer families will be accommodated. Methods. Pursuant to the development of both studies, two feasibility surveys were conducted to determine whether patients would grant access to their FDRs and whether the FDRS identified by these patients would be receptive to the telephone intervention. Results. Approximately 80% (106 of 132) of breast cancer patients agreed to provide access to their eligible FDRs when contacted on-site at participating hospitals and clinics. Of those subsequently selected for telephone follow-up (n = 95 or 90%), 80% (n = 76) were successfully contacted by telephone, and of these 97% (n = 74) provided the names and telephone numbers of their FDRs. Among colorectal cancer patients contacted on-site (n = 46), 96% (n = 44) agreed to provide access to their FDRs, and of those contacted by telephone (n = 33 or 75%), 91% (n = 30) provided the requested information about their FDRs. Once contacted, 95% of breast cancer FDRs (55 of 58) and 91% of colorectal cancer patients (51 of 56) endorsed the intervention strategy. Conclusions. It is argued that this intervention, if proven effective, could provide an exportable strategy for reaching large numbers of high-risk individuals to promote cancer screening.