The United States Biological Human beta Amyloid 1-40 (Hu A beta40) ELISA kit is a solid phase sandwich Enzyme Linked-Immuno-Sorbent Assay (ELISA). A monoclonal antibody specific for the NH2-terminus of Hu b-amyloid has been coated onto the wells of the microtiter strips provided. During the first incubation, standards of known Hu b-amyloid 40 content, controls, and unknown samples are pipetted into the wells and co-incubated with a rabbit antibody specific for the COOH-terminus of the 1-40 b-amyloid sequence. This COOH- terminal sequence is created upon cleavage of the analyzed precursor. Bound rabbit antibody is detected by the use of a horseradish peroxidase-labeled anti-rabbit antibody. After washing, horseradish peroxidase-labeled anti-rabbit antibody (enzyme) is added. After a second incubation and washing to remove all the unbound enzyme, a substrate solution is added, which is acted upon by the bound enzyme to produce color. The intensity of this colored product is directly proportional to the concentration of Hu A beta40 present in the original specimen.