Objective:To observe the change of apoptosis of nucleus pulposus cells cultured in vitro under hypoxic condition and different hydrostatic pressure.Methods:The human degenerative nucleus pulposus cells were cultured in vitro and randomly divided into 2 groups according to hypoxic condition:the hypoxia group and the normal oxygen partial pressure group.While the nucleus pulposus cells were randomly divided into three groups according to different hydrostatic pressure:the control group without pressure,the 50 kPa pressure group and the 100 kPa pressure group.The change of apoptosis of nucleus pulpo-sus cells was detected by methyl thiazolyl tetrazolium(MTT)method and terminal dexynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)assay.Results:As compared with that in normal oxygen partial pressure group,the proportion of survival nucleus pulposus cells in hypoxic group increased,while the number of apoptotic cells decreased.Under different hy-drostatic pressure,there was no statistically significant difference regarding the apoptotic positive rate of nucleus pulposus cells between the 50 kPa pressure group and the control group (P >0.05 ).However,the apoptosis positive rate in the 100 kPa pressure group increased by 3 1 .65%,compared with that in the control group,and the difference was statistically significant (P <0.01).Conclusions:Hypoxic condition,as well as low pressure condition,can reduce the occurrence of apoptosis of nu-cleus pulposus cells.