Iron is an essential trace element for mammals. However, small portion of iron exist as non-transferrin-bound iron (NTBI) in blood or labile iron pool (LIP) in cells that induce oxidative strees in human. It is well known that iron plays an important role in many diseases such as neurodegenerative diseases (Alzheimer’s disease, Parkinson’s disease and others) and carcinigenesis. In HVC hepatitis, patients recieve blood removal treatment to reduce the body iron. The effect of bllod removal from cancer patients is also being studied intensively. While immature cells are depend on iron for the proliferation and iron is essential, differentieted cells demand relatively less iron. We have found that immature PC12 cells are labile for iron-induced oxidative strees, but differentiated neuronal PC12 cells are resistant. We are studing the relationship between cell differentiation and tolerance of iron-induced oxidative stress.