Background: We recently designed a cationic polymer called histidylated polylysine made of polylysine partially substituted with histidyl residues which become protonated at slightly acidic pH. This polymer is thought to induce the leakage of acidic vesicles containing plasmid/histidylated polylysine complexes. Methods and results: Here, we have analyzed the ability of histidylated polylysine to transfer reporter or CFTR genes into immortalized cystic fibrosis airway surface epithelial cells (ΣCFTE29o‐ cells) and airway gland serous cells (CF‐KM4 cells) which are both important targets for cystic fibrosis gene therapy. The luciferase reporter gene expression measured after gene transfer with histidylated polylysine into both cell lines was quite high and similar to that obtained with commercially available vectors. In addition, the level of expression was not dependent on the presence of a membrane disrupting agent such as chloroquine. Histidylated complexes were present in slightly acidic non‐lysosomal cellular compartments as shown by a cytological approach using biotinylated plasmid, lysosome‐specific antibodies and confocal microscopy. Histidylated complexes appeared to be of small size when prepared at low ionic strength and formed aggregates upon increasing the ionic strength. However, aggregate formation was prevented by the addition of 10% fetal bovine serum. Gene transfer efficiency varied with the size of the complexes and decreased when small particles were used. Conclusions: These results suggest that histidylated polylysine may be an efficient non‐viral vector for gene transfer into cystic fibrosis airway surface epithelial cells and airway gland serous cells. Copyright © 2000 John Wiley & Sons, Ltd.