A technique used to identify specific molecules in different kinds of tissue. The tissue is treated with antibodies that bind the specific molecule. These are made visible under a microscope by using a color reaction, a radioisotope, colloidal gold, or a fluorescent dye. Immunohistochemistry is used to help diagnose diseases, such as cancer, and to detect the presence of microorganisms. It is also used in basic research to understand how cells grow and differentiate (become more specialized).
Source: The National Cancer Institute's Dictionary of Cancer Terms (http://www.cancer.gov/dictionary)