Abstract: The present invention relates to improved methods for introducing nucleic acid into cells by first complexing the nucleic acid with a selected polycationic oligomer which neutralizes the negative charge of the nucleic acid, and then contacting the cell with the complex facilitating uptake of the nucleic acid into the cells as a complex with the oligomer. The methods are preferably applied to introduction of nucleic acid into eukaryotic cells, and more preferably into human cells. The invention also relates to methods of introducing antisense and triplex-forming oligonucleotides into prostate cancer cells to inhibit expression of proteins associated with (or that promote) malignancy and to inhibit cell growth or proliferation. More particularly, the invention relates to a method for inhibiting the expression of the HER-2/NEU protein in prostate cancer cells and to a method for inhibiting prostate cancer cell growth or proliferation.