As programmed cell death (PCD) or apoptosis has emerged as an important 
regulator of development and homeostasis in multicellular organisms, methods to 
quantify apoptosis and to distinguish it from necrosis have been developed. This 
unit presents a set of assays for these purposes, many of which are technically 
very simple and ideally suited to the study of hematopoietic cells. The first 
basic protocol allows the qualitative and quantitative assessment of apoptosis 
in lymphocyte cell cultures using light or fluorescent microscopy. Three 
protocols follow that are designed to detect nuclear DNA fragmentation and 
support protocols describe methods to radiolabel the DNA and cytoplasm of the 
cells to be tested. Techniques that quantitate apoptotic cells using flow 
cytometry are then described and support protocols provide methods for priming T 
cell clones and freshly isolated lymph node cells, respectively, for T cell 
receptor (TCR)-induced apoptosis. Quantitative detection of DNA fragmentation in 
apoptotic cells is also described. TdT-mediated dUTP-biotin nick end-labeling 
(TUNEL) methods are provided for the detection of apoptotic cells, along with 
procedures for the flow cytometric quantitation of apoptotic cells using TUNEL, 
and TUNEL, staining of tissue sections to identify apoptotic cells. Since much 
remains incompletely understood about the molecular pathways of programmed 
death, and it is probably best to perform more than one of the basic protocols 
to confirm an observation of apoptotic cell death.