Few techniques have approached the high resolution afforded by immunoelectron microscopy using gold markers for the detection of specific cellular proteins and other molecules (1) or by post-embedding procedures (2). In principal, a primary antibody to a particular protein, which has been fixed, embedded, and placed on a grid, is identified by a host-specific secondary antibody conjugated to a gold particle of defined size. The gold particle identifying the targeted protein is then detected by electron microscope observation. This method has undergone a steady development over the past few years, because it uniquely meets the need to precisely assign macromolecules to specific locations and domains within both tissues and cells. It has also been used to reveal antigens that may be present in low or trace amounts and thus, has contributed to a greater understanding of functional specialization domains within cells and tissues. Its advantages over light microscopic immunocytochemistry and confocal immunofluorescence localization studies are that it can be carried out on very minute specimens and that it can provide a permanent record for quantitative analyses of multiple domains. Its disadvantage is that, because of the small tissue size, more sampling is needed and more expertise is required in handling, thus requiring more overall experimental time. Additionally, the operation of an electron microscope (EM) can result in prohibitive costs.