The loss of cell volume or cell shrinkage, termed apoptotic volume decrease (AVD), is a classical characteristic of apoptosis. Microscopy, Coulter electronic sizing, and/or flow cytometry has traditionally been the means to measure this characteristic of apoptosis. Although electronic cell sizing allows for precise determination of changes in cell size, these measurements provide data on the entire population of apoptotic cells. In contrast, flow cytometry examines and separates unique populations of apoptotic cells based on the light-scattering properties of the cells to determine alterations in cellular dimensions. However, this technique does not provide exact measurements of cell size and volume. The Cell Lab Quanta SC flow cytometer combines the power of electronic sizing with the ability to isolate and examine unique populations of apoptotic cells to determine exact changes in cell size as they undergo cell death. This chapter describes several methods for using the Cell Lab Quanta SC to study AVD during apoptosis.