In the 5 years since the cloning of the cystic fibrosis (CF) gene, several experimental trials of CF carrier screening have been performed and reported. Two particular groups have been targetted: young adults near reproductive age, and pregnant women. The three trials directed at young adults have shown that the method of presentation is a major determinant of take-up rates; an offer of screening by personal intervention gives high acceptance while an offer by mail or leaflet produces disappointing results. There is a strong suggestion that screening is being foisted on an unreceptive group, whose response is one of politeness rather than conviction--'supply push' rather than 'demand pull'. Trials of screening during pregnancy have been more extensive and more satisfactory. Two models have been tested. In sequential delivery, women are screened first and their partners only tested when they are found positive for CF alleles. This can lead to anxiety, during the period while positive women await their partner's result. In couple screening both partners agree to be treated as a unit and reported as high risk only when both are positive. In other situations they are regarded as negative. Couple screening has turned out to be remarkably efficient, trouble-free and consumer-friendly, and has become the method of choice for integration into routine health care.