The first phase I study of cystic fibrosis gene therapy using cationic liposomes to deliver the cystic fibrosis conductance regulator gene to the nose reported partial and transient correction of the nasal transepithelial ion transport defect, While encouraging, further improvements will be required if this form of treatment is to be of therapeutic value. We tested a new formulation, pCMV-CFTR-DOTAP. The complex is stable for 10 days and effective at correcting the electrophysiological deficit in the trachea of CF mutant mice at 8 or 9 days after intratracheal instillation. Reliable protocols for consistent detection of as few as 10 molecules of CFTR mRNA and DNA in nasal brushing samples are described, Both vector and DNA have been produced to Good Manufacturing Practice standard, Nasal potential difference measurements developed at the National Heart and Lung Institute to assess the CFTR ion channel activity in CF patients replicated well at the Scottish Adult Cystic Fibrosis Service. The SPO fluorescence assay for halide ion conductance in nasal brushings has also been tested. These establish baseline conditions in the Scottish CF cohort from which evidence for correction can be judged under clinical trial conditions. These studies formed the basis for regulatory approval of a randomised, placebo controlled double-blind phase I research study.