Efficient and minimally invasive drug delivery systems have been developed to treat intractable human diseases. One approach has been the development of chimeric vector systems combining at least two different vector systems. Based on this concept, chimeric drug delivery systems that combine viral and non-viral features have been developed. Fusigenic non-viral particles have been constructed by conferring viral fusion proteins onto non-viral vectors. HVJ (hemagglutinating virus of Japan; Sendai virus)-liposomes were constructed by the combination of DNA-loaded liposomes with a fusigenic envelope derived from HVJ (hemagglutinating virus of Japan, Sendai virus). Reconstituted HVJ-liposomes were also developed by the insertion of isolated fusion proteins of HVJ into DNA-loaded liposomes. Recently, the technology has been developed to incorporate macromolecules directly into inactivated HVJ particles without liposomes. The resulting HVJ envelope vector introduced plasmid DNA, efficiently and rapidly into both cultured cells in vitro and organs in vivo . Furthermore, proteins, synthetic oligonucleotides and drugs have also been effectively introduced into cells using the HVJ envelope vector. The HVJ envelope vector will be a promising tool for both ex vivo and in vivo gene therapy experiments.