The ability to identify apoptotic cells within a complex population is crucial in the research and diagnosis of normal physiology and disease states. The Cellscan mark S (CS-S) cytometer was used in this study to detect intracellular fluorescence intensity and polarization (FI and FP) in several well-established models of apoptosis: Following spontaneous apoptosis, as well as glucocorticoid or anti Fas-induced apoptosis, CS-S individual cell-based analysis revealed the appearance of a cell cluster characterized by low FI and high FP. Temporal analysis of annexine V binding and FP measurements following DXM treatment showed that hyperpolarization preceded phosphatidylserine appearance on the outer plasma membrane. The early increase in FP was found to be dose dependent and inversely related to cell diameter. Cell dehydration and alteration of plasma membrane transport properties, both occurring during early stages of apoptosis, may be involved in the phenomena of intracellular fluorescein hyper-polarization in apoptosis.