Amperometric feedback and potentiometric modes of the scanning electrochemical microscope (SECM) have been used to image the topography and map redox and acid-base activities in single mammalian cells. The topographic images of cells were obtained using hydrophilic redox mediators, which cannot penetrate the cell membrane. In contrast, with a hydrophobic mediator one can map redox reactivity with a micrometer or submicrometer spatial resolution. The images obtained with oxygen used as a redox mediator show the distribution of the diffusion rate of oxygen in the cell membrane and inside the cell. The acid release by the cell was imaged with a Sb tip in a potentiometric mode, and the possibility of redox and pH imaging of the same cell with same tip is demonstrated. Significant differences were detected in the redox and pH images of normal human breast epithelial cells and metastatic breast cancer cells.