A dielectrophoresis (DEP) cell profiler, with concurrent FACS measurements, was used to monitor the morphological changes of Jurkat T-cells as they progressed through chemically induced apoptosis using etoposide. The cell 'physiometry' profiling technique measures the radius and the so-called DEP crossover frequency f(xo) of individual cells in a suspension, and this information was used to determine the effective plasma membrane capacitance of each cell. Control cells (n=526) exhibited a dynamic spread of f(xo) values, ranging from 50 to 250 kHz, and as apoptosis progressed over 6 h, the upper value for f(xo) progressively increased and extended beyond 500 kHz. This corresponded to a reduction in plasma membrane capacitance from 13.34 (+/-2.88) to 10.49 (+/-4.00) mF/m(2), and reflected a general smoothing of the membrane through loss of microvilli, for example. This is in broad agreement with previously reported studies of HL-60 cells undergoing apoptosis, but the authors' observation of a dynamic spread of f(xo) values does not agree with the earlier report that the f(xo) values for viable and apoptotic cells fall into two separable, relatively narrow, frequency bands. This has implications when devising protocols for the efficient DEP separation of viable, apoptotic and necrotic cells.