We have assessed the effect of screening for cystic fibrosis (CF) carrier status on anxiety levels, attitudes, knowledge and actions of participants in a pilot programme conducted through primary health care services. Over 3000 individuals were screened and 100 carriers with no previous family history were identified. Varying degrees of anxiety were found to be associated initially with a positive result, but most of this was allayed by genetic counselling, and we find no adverse long-term psychological consequences in carriers. Most discussed carrier status with their partner (89%), parents, other relatives and also with friends; 87% of partners to whom testing was suggested have been screened. Those testing positive indicated that knowledge of carrier status would be considered in future reproductive decisions, and after 6 months carriers retained a reasonable level of knowledge about CF and its inheritance. Carriers and non-carriers uniformly approve of screening and are glad to have been tested. Knowledge of CF in the sample of non-carriers has also increased after testing, suggesting screening may improve understanding of CF among the entire target population. Fears of possible social costs of screening may be ill-founded.