Apoptotic cells possess specific morphological and biochemical markers. Various 
methods have been developed to detect apoptosis based on these markers. One of 
the most common is the fragmentation of genomic DNA. In addition to 
electrophoresis for the identification of the characteristic 200 base pair 
ladders and terminal deoxyribonucleotidyltransferase-mediated dUTP-biotin nick 
end-labeling, DNA content analysis is often employed. This technique is based on 
the fact that permeablized apoptotic cells release fragmented DNA, resulting in 
DNA content that is less than that in live diploid cells. Although widely used, 
we have found that the number of apoptotic cells detected by DNA content 
analysis is often lower than that detected by other methods. We have developed a 
simplified version of the flow cytometry-based protocol that detects a number of 
apoptotic cells closer to that detected by other methods, and which requires a 
dramatically reduced number of cells. In addition, this simplified protocol 
allows preparation of a large number of samples at the same time.