Since the cytotoxic activity of PAMAM-drug-trastuzumab conjugates and free drugs was previously tested on HER-2-positive (SKBR-3) and negative (MCF-7) human breast cancer cell lines, the same cell lines were used in the present study to investigate the influence of the conjugates and drugs on mitochondrial membrane potential, the intracellular reactive oxygen species generation, caspases activity, cell cycle and ability to induce apoptosis or necrosis. Here, ERBB2 is linked to breast cancer.