Provided are compositions and methods useful in the diagnosis of Alzheimer's Disease (AD). The methods involve immunologically testing biological samples for an amount of high molecular weight kininogen (HK) and cleaved high molecular weight kininogen (HKc), wherein determining less HK relative to a normal control, or determining more HKc relative to a normal control, or a combination thereof, aids in diagnosis of AD. Hybridomas and monoclonal antibodies bind with specificity to either HK alone, or to both HK and HKc. Kits for use in immunological AD testing using the mAbs are also provided.