The present invention discloses methods for inducing regression of a tumor in a subject by administering a pharmaceutical composition comprising a lentogenic strain of Newcastle disease virus (NDV). A preferred viral strain of NDV for inducing regression of a tumor in a subject is a clonal strain of NDV, the NDV HUJ. The methods of the present invention are particularly useful for inducing regression of tumors in patients unresponsive to conventional anti-cancer therapies.