The aim of this study was to compare six methods of detecting apoptosis induced by extracellular adenosine triphosphate （ATP） in human leukemic lymphocytes with purinergic P2Z receptors.These methods used were electron microscopy（EM）

detection of internucleosomal DNA fragmentation by agarose gel electrophoresis

autoradiographic analysis of DNA fragmentation

in situ labeling of DNA strand breaks with fluorescein dUTP and exogenous terminal deoxynucleotidyl transferase （TUNEL）

quantitation of 3 ends of DNA breaks by labeling with α 32 PdCTP（TdT assay）

and quantitation of apoptotic cells with fluorescein annexin V using flow cytometry（FCA）.We found EM and detection of DNA ladder pattern by agarose gel electrophoresis to be specific

but lacking in sensitivity. The combination of autoradiography and gel electrophoresis gave an increase in sensitivity of at least 50 fold although

of all the methods

the TdT assay was shown to be most sensitive. The four methods for quantifying apoptosis EM

FCA

TUNEL and TdT assay proved to be reliable and gave statistically similar results on apoptotic lymphocytes. These observations indicate it is essential to combine specific

sensitive and quantitative techniques in detecting apoptosis.