The changes in the dielectric properties of cells that occur during their exposure to various lethal environmental stresses were measured using both dielectric spectroscopy and dielectrophoresis. It is shown that the dielectric properties of both dying and dead yeast cells were strongly dependent on the method used to induce cell death. Methods which directly affected the membrane permeability, and consequently the membrane conductivity and internal conductivity, resulted in large changes in the suspension capacitance and dielectrophoretic behaviour, whilst methods which affected the cell interior but had little effect on the cell membrane resulted in few or no changes in the dielectric properties of the cells. The findings indicate that, depending on the method by which cell death is induced, dielectric spectroscopy may not always be able to observe differences between viable and non-viable cells, and that dielectrophoresis will not always be able to separate viable from non-viable cells. (C) 2008 Elsevier Inc. All rights reserved.