The search is ongoing for a reliable serum biomarker for AD. The level of iron is elevated in the brain of Alzheimer's disease (AD) patients. Our studies have demonstrated that the level of the iron transport protein, p97, is increased in the serum of AD patients but not in various control groups. These results have recently been confirmed by another laboratory who extended our findings by demonstrating that p97 is not elevated in other neurodegenerative diseases. This qualifies p97 as a potentially powerful biomarker specific for AD. Although the relationship between increased level of iron and p97 in the AD brain is not well understood, our research supports the hypothesis that p97 over-expressed by senile plaque associated reactive microglia is exocytosed and appears in blood. The relationship between elevated levels of serum p97 and AD, together with the possible future clinical application of p97 are considered in this report.