Methods used in transient transfection of cells may alter cellular signaling pathways that in turn may lead to misinterpretation of the results. A variety of genotoxic agents cause the accumulation of the p53 protein leading to either apoptosis or growth arrest. Here we report the effect of electroporation and carrier DNA on the stability, cellular localization, and transcriptional activity of p53. We show that electroporation leads to p53-dependent and also p53-independent cell-cycle arrest and apoptosis. At the same time a chemical agent polyethylenimine that is also used for transient transfection of cells causes neither upregulation of p53 nor cellular response.