Cellular homoeostasis involves a continuous interaction between the cell and its microenvironment. As such, active and passive transport of ions, nutrients, molecules and water are the basis for biochemical–physical cell life. These transport phenomena change the internal and external ionic concentrations, and, as a consequence, the cell membrane’s electric potential and the pH. In this paper we focus on the relationship between these ion transport-induced pH and membrane voltage changes to highlight their impact on carcinogenesis. The preliminary results suggest a critical role for Cl− in driving tumour transformation towards a more malignant phenotype.