Primary care physicians have been very cooperative in referring screened patients to the two designated CF centers in Wisconsin--the University of Wisconsin Cystic Fibrosis Center, and the center at the Medical College of Wisconsin in Milwaukee--and their help has made this study possible. By 1990, we anticipate that meaningful clinical comparisons between the screened and control groups will be possible, and at that time we can begin to obtain some definitive answers concerning the benefits and potential risks of neonatal screening for cystic fibrosis. At this time, it would be premature to make a decision concerning the efficacy of screening for cystic fibrosis for the State of Wisconsin. It is very important that the study go to completion before making conclusive recommendations. We are eager to meticulously document the natural history of CF by following study patients for a long time. Answers to questions concerning rate of decline of the IRT value in true positives, psychosocial risks of screening to true positives, effect on future reproductive plans, and the cost effectiveness of the screening program will not be available for at least two more years. False positive IRT results seem to be related to perinatal asphyxia. We postulate the mechanism is ischemia in the pancreas related to hypoxia during the perinatal period leading to transient release of trypsin from the pancreas into the bloodstream. Decline of the IRT result over time is of great interest because a repeat blood sampling approach would hopefully eliminate several false positives.(ABSTRACT TRUNCATED AT 250 WORDS)