Estimates of the newborn frequency of cystic fibrosis in different Caucasian groups range from 4 times more to 40 times less common than the generally accepted figure of 1:2000. Current meconium screening trials which may be effective in populations with the incidence equal to or greater than 1:2000, may be useful for populations with an incidence as low as 1:7000 only after maximum improvement of the methods. Once the true incidence or the variable incidence is proven for Caucasian populations, screening trails in Negro, Oriental and Indian populations will be required.