One of the areas in which the use of immunocytochemistry has had the greatest impact is in the examination of tissue in the medical pathology laboratory. Immunocytochemistry or actually immunohistochemistry in the pathology laboratory enhances the study of diseased tissue. It is important in studying disease to obtain and process the tissue as quickly as possible. The reason for this is so that the cellular constituents can be preserved as completely as possible. As is the case with any solid piece of tissue, the smaller the piece, the easier it is to preserve the cellular constituents. The varied types of tissue also determine, to an extent, preparation protocols because some types require a more specialized form of preservation than do others. Some specimens, like bone, require many days for proper fixation, whereas other looser connective tissues are preserved in a matter of hours by simple immersion fixation. It should be mentioned, though, that depositing large organs, like whole brains, in buckets of fixative may provide fine cellular detail, but will probably result in the loss of some labile brain proteins desired for study (1 ). The individual who actually obtains the specimen is an important aspect of tissue processing. This individual needs to remove the sample quickly and, before much autolysis occurs, immediately place the correctly sized (small) sample into the desired fixative.