Up to now, 16.338 IRT-measurements have been carried out on dried blood spot specimens; 15.505 of them were taken in the first week of life. Related to a provisionally chosen cut-off point of 750 ng/ml, 134 newborns (= 0.86%) showed an elevated IRT-value and subsequently were recalled between the fourth and sixth week of life for a second IRT-determination. Twenty-five out of 116 reinvestigated children again showed an elevated value, as based on likewise provisional, age-dependent reference values. Four of these children subsequently were identified as CF patients by sweat testing. So far, we did not encounter any false-negative IRT values. We also commenced to establish a profile of reference values for the first twelve weeks of life; as yet, there are not enough data for definitely defining these limits of normality. In conclusion, IRT-screening appears to be a reliable method for identifying CF patients in the newborn period. Our preliminary results indicate an incidence of CF of 1 to 3880 in the southeast of Austria.