The highly condensed chromatin of mammalian spermatozoa is usually considered to be biologically inert before fertilization.However,we have demonstrated that even in this compacted state,sperm chromatin is subject to degradation at open configurations associated with the nuclear matrix through a process we have termed sperm chromatin fragmentation (SCF).This suggests that a mechanism exists to monitor the health of spermatozoa during transit through the male reproductive tract and to destroy the genome of defective sperm cells.