Methods were developed to achieve targeted eradication of the erbB-2 oncoprotein using gene constructs encoding anti-erbB-2 intracellular single-chain antibodies. This method of genetic intervention caused a marked cytocidal effect in erbB-2-overexpressing human ovarian tumor cells. Evaluation of the mechanistic basis of this phenomenon demonstrated that programmed cell death had been induced. Significantly, no cytocidal effect was observed in non-erbB-2-overexpressing tumors. The induction of apoptosis could be shown to be secondary to the intracellular antibody-mediated ectopic localization of the erbB-2 oncoprotein. Thus, the strategy of selective oncogene "knock-out" using intracellular antibodies represents a novel anticancer gene therapy strategy that offers the potential to achieve highly specific, targeted eradication of human tumor cells.