To demonstrate the approach, we developed a screening test for carriers of cystic fibrosis (CF) that tests for all 25 mutations and the reflex targets in the widely used panel (19 ) and also tests for 394delTT and 3199del6. 394delTT is the second most prevalent mutation in populations with Nordic heritage and may be important in Wisconsin, where testing was performed. 3199del6 was added because several lines of evidence indicate that 3199del6 is a disease-causing mutation and may replace I148T (20 ) .