Several advances in non-viral gene transfer technology have been reported over the past year. Cationic lipids have been successfully used to deliver genes in vivo, providing a clear alternative to recombinant viruses. In addition, investigators have demonstrated that direct application of DNA via injection or particle bombardment can be used for vaccination. Analysis of the mechanisms employed by viruses to invade cells has demonstrated a crucial role for membrane-active proteins or peptides in the entry process. Several non-viral systems that include membrane-active elements are now available.