Use of low abundance analytes in whole tissue homogenates has been realized with the development of assays in which a specific analyte is captured and detected using immunological reagents. One of the many advantages of analyte immunoassay in crude homogenates is its relative simplicity, allowing high throughput analysis of samples. In this unit, some major key determinants in sample and standard preparation and handling are described that have been shown to improve the performance and reliability of these assay systems. The ELISA assay of amyloid peptides from brain tissue is described as an example, since the protocols for this analysis exemplify many of the techniques and problems that are encountered in the development of new assays.