A quadrant dot blot analysis of peripheral blood mononuclear cells stained for apoptosis using an annexin V detection of phosphatydyl serine expression along the x-axis, counterstained with propidium iodide to detect late apoptotic or necrotic cells. Control cells are represented on the left hand plot and cells undergoing apoptosis are represented in the right hand plot. The lower left quadrant are viable non-apoptotic cells; the lower right is apoptotic cells binding annexin V; the upper right are late apoptotic cells that are binding annexin V and taking up propidium iodide. The upper left would contain cells that take up propidium iodide but do not bind annexin V. These cells would most likely be necrotic.