The term apoptosis describes the predictable structural changes associated with many forms of programmed cell death. One of the first visible events of apoptosis is the collapse of the nucleus. Nuclear degradation is manifested by digestion of chromatin into nucleosome-sized fragments or multiples of these. This digestion of DNA is enzymatic, and several attempts have been made to characterize apoptosis-specific endodeoxyribonucleases. Although there are strong candidates for such enzymes, direct evidence for their role in apoptosis is yet to be provided.