The role of bivalent cations and choli ne in ATP-induced apoptosis via P2Z pur i noceptor was investigated in human leu ke mic lymphocytes. In vitro exposure of le ukemic lymphocytes with P2Z receptor s to 1 mmol/L ATP or 0.1 mmol/L benzoyl benzo ic ATP(BzATP) for 8 h in the prese nce of choline, 1 mmol/L Mg2+ or oth er biva lent cations, and ATP-induced DN A breaks , associated with apoptosis wer e quantif ied by TdT assay. We observed that (1) E xtracellular Mg2+ or Ca2 + stimulat ed ATP-induced DNA fragmenta tion in a do se-dependent manner, and th e compatible evidence was provided by t he inhibition of ATP-induced DNA fragme ntation in the present of EGTA or EDTA; (2) ATP-induced DNA fragmentation was completely inhibi ted by 1 mmol/L Zn2+ ;(3)ATP-induced D NA breaks were not af fected by Ba2+, Sr2+, Co2+ whe n they were substitu ted for extracellul ar Mg2+ or Ca2+ ;(4)Choline, an in hibitor of phospholipa se D(PLD) stimula ted by ATP through P2Z receptor in huma n lymphocytes, was also a partial inhib itor of ATP-induced DNA f ragmentation, and the results were confi rmed by flow cytometric analysis (FCA); (5)ATP-induc ed DNA fragmentation was com pletely obl iterated when the temperature was lower than 10℃. These results sugge st that t he endonuclease and PLD may be involved in ATP-induced apoptosis in hum an lymp hocytes via P2Z receptor.