The primary goal of mass screening programs for cystic fibrosis carriers should be to allow people to make more informed reproductive decisions. However, previous experience with genetic screening programs, including those for phenylketonuria and sickle cell disease, have revealed complex problems including error, confusion, and stigmatization. These problems could be greater with cystic fibrosis, since more than 8 million Americans may be carriers and entrepreneurial interests can be expected to promote screening in what could become a billion-dollar industry. The present frequency of the detectable mutation (ΔF508), 75%, will complicate the counseling process. The sensitivity of the test to detect at-risk couples would be 56%. The cost of screening could be as much as $2.2 million for each cystic fibrosis birth avoided. Regardless of improvements in the detection rate, implementation of population screening should be delayed until pilot studies that demonstrate its safety and effectiveness are completed. While studies are in progress, preconception testing should be offered to adult relatives of cystic fibrosis patients as part of a comprehensive program following institutional review board approval for "compassionate use." The purpose of such review should be to ensure that strict standards of informed consent, education, quality control of the testing procedure, and counseling are followed. Primary care physicians who are unable to offer screening as part of such a comprehensive program should refer high-risk patients who would like to consider being tested to established centers.