The prospect of harnessing the cytocidal properties of viruses for targeted attacks on cancer cells, has prompted an ongoing development in the design of manipulated adenoviral vectors. The adenovirus is efficient in gene transfer, and serves as vector in clinical gene therapy. But its genome contains genes that code for products that bind to and inactivate tumor suppressor gene products, and it has been demonstrated that the deletion of the early genes produces oncolytic adenoviruses that replicate in cancer cells and kill them. New forms of oncolytic viruses with deletions of some viral genes like E1B and being armed with anticancer cDNAs contributed to enhanced cytotoxicity of adenoviral vectors. The engineering of the adenoviral vector could be useful for the development of biotherapeutic agents, as it could expand the list of anti-oncogenes used in anticancer biotherapy.