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To verify the inhibitory or protective effects of light-emitting diode(LED) irradiation on apoptotic cell death induced by CoCl2, human SH-SY5Y cells were treated with CoCl2 and LED were used to irradiate the cells. In the cell viability assay, cells were died slowly from 50 μM to 250 μM and about 50% of cells died after 12 hours at 400 μM of CoCl2. The Diff-Quik staining revealed that cells showed condensation of DNA and blebbing of the cell membrane. The DNA fragmentation assay revealed the DNA fragmentation, which is another apoptosis marker, occurred in cells treated with 400 μM CoCl2 for 16 hours. In the western blot for HIF-1α, HIF-1αwas expressed after 3 hours from induction and peaked maximally at 16 hours. In the cell viability assay of the effects of LED irradiation (at 590 nm for 1 hour 20 minutes), the cells showed more proliferation (about 20%) than the control group. The RPA assay of various apoptosis-related molecules showed that pro-apoptosis molecules such as Bax, Bak, and Bid were upregulated in the CoCl2 treatment group. This means that the apoptotic cell population was increased. However there was some significant changes in LED irradiated cells. In the CoCl2-treated LED irradiation group, those molecules were down-regulated more than in the only CoCl2-treated group. These results have shown that CoCl2 may induce apoptotic cell death in human SH-SY5Y neuroblastoma cells. And LED irradiation has a positive effect on apoptotic cells by down-regulation of pro-apoptotic molecules.