Cytotoxic T lymphocytes, and other death-inducing agents, have at least two different ways of killing their targets: drilling holes in the target cell membrane, or triggering the targets to commit suicide. The JAM Test is a method that measures the DNA fragmentation that accompanies cell suicide. We label target cells with radioactive DNA-precursor nucleotides and harvest them onto fiberglass filters, which trap large pieces of DNA but pass smaller fragments of apoptotic cells. As a general measure of apoptosis, the JAM Test described here is faster (can be completed in 4 h [or less if labeling is done the night before]), more quantitative, easier, more sensitive, more flexible and cheaper than most other current assays of apoptosis. The P-JAM, also discussed, additionally allows for assessment of death in cells that don't fragment their DNA, and allows for assays of agents that induce cell stasis rather than death.