Impedance measurements on arrays of microelectrodes can provide information about the growth, motility, and physiology of cells growing on the electrodes. In this talk, we report recent results obtained for the growth of 3T3 mouse fibroblasts and HCT116 human cancer cells on gold electrodes approximately 0.4 mm2 in area. Cells produce a characteristic peak in the impedance change plotted as a function of frequency. With the aid of electrical modeling of the cell-electrode system, the details of the changes in the measured impedance can be correlated to the cell size, fractional electrode coverage, and cell-electrode gap. In particular, comparison of impedance measurements of these two cell types show clear differences in the growth rate and the ratio of the cell-electrode gap to the cell size. In addition to presenting these experimental results illustrating the utility of electrode impedance measurements, we will outline the issues encountered when electrodes are scaled to cell size and incorporated into a matrix-addressed array.