Nucleases involved in the generation of the internucleosomal, 200-bp fragments have been variously identified as DNaseI, DNaseII, and several other proteins. 40-42 However, an observation that is not controversial is the generation of 3′-OH groups on the fragmented DNA.43 These new 3′-OH groups can be identified by in situ labeling and forms the basis of the histochemical ISEL(in situ end labeling) method to detect apoptotic cells. The ISEL technique relies on the labeling of DNA by terminal deoxynucleotidyl transferase (TdT) or DNA polymerase. Based on the enzyme that is used to label the DNA, the method is either called TUNEL (TdT mediated dUTP nick end labeling) or ISNT (in situ nick translation). 14,44,45