Intact cells of the yeast Saccharomyces cerevisiae were transformed with exogenous DNA by incubating the cells with plasmid in the presence of polyethylene glycol (PEG), which has been shown to be required, although the underlying has not been elucidated. In this study, we found that incubation of the S. cerevisiae cells with PEG was not only required for the PEG-dependent transformation but also enhanced transformation, suggesting that PEG might cause an intracellular response. To understand the response, microarray and metabolome analyses were conducted. We found that incubation of the cells without PEG caused up-regulation of several genes, including those which are involved in carbon source metabolisms, e.g. fatty acid metabolism, yielding acetyl-CoA and those involved in stress-response. Contrary to this, incubation of the cells with PEG gave no transcriptional change. These microarray data were supported by the results of metabolome analysis for anionic metabolites, implying that the physical effect of PEG on cell membrane, rather than the effect of PEG itself on the intracellular response, could cause high transformation in the PEG-dependent transformation.