C ationic lipids show promise as vectors for transfer of CFTR cDNA to airway epithelia of patients with cystic fibrosis (CF). However, previous studies have not compared the effect of DNA-lipid to DNA alone. Recently, we developed a formulation of plasmid encoding CFTR (pCF1-CFTR) and cationic lipid (GL-67:DOPE) that generated greater gene transfer in mouse lung than previously described DNA-lipid vectors. Therefore, we tested the hypothesis that DNA-lipid complexes were more effective than DNA alone at transferring CFTR cDNA to airway epithelia in vivo. We administered complexes of DNA-lipid to one nostril and DNA alone to the other nostril in a randomized, double-blind study. Electrophysiologic measurements showed that DNA-lipid complexes partially corrected the Cl- transport defect. Importantly, the pCF1-CFTR plasmid alone was at least as effective as complexes of DNA with lipid. Measurements of vector-specific CFTR transcripts also showed gene transfer with both DNA-lipid and DNA alone. These results indicate that nonviral vectors can transfer CFTR cDNA to airway epithelia and at least partially restore the Cl- transport defect characteristic of CF. However, improvements in the overall efficacy of gene transfer are required to develop a treatment for CF.