An immortalized cell line was created from a primary culture of bronchial epithelia isolated from a patient with cystic fibrosis. The culture was transformed with a hybrid virus, adeno-12-SV40, which has been used successfully on a number of different human epithelial tissues. The transformed bronchial epithelial cells have the following characteristics. (1) Cyclic adenosine monophosphate (cAMP) is stimulated by beta-adrenergic agonists. (2) Outwardly rectifying Cl- channels are present on the apical cell membrane. These channels can be activated by depolarizing voltages but not by protein kinase A or C. (3) Keratin is present by immunofluorescence, and this is consistent with the epithelial origin of the cells. (4) The SV40 large T antigen is present as demonstrated by immunofluorescence. (5) Multiple karyotype analyses show modal chromosome number to be 80 to 90. There are an average of four chromosome 7 per cell. (6) The phenylalanine508 deletion in the gene coding for the cystic fibrosis transmembrane regulator is present on at least one chromosome. The cells can be grown in multiple passages, contain the abnormal regulation of the secretory Cl- channel, and should be an appropriate substrate for studies of the mutant cystic fibrosis transmembrane regulatory protein and its interaction with the Cl- channel.