Fresh tissue must be preserved in some manner before analysis because the substances to be tested in the tissue are often labile and cannot withstand analytical procedures without first being preserved. The best method for antigen preservation in immunocytochemical analysis is freezing. Freezing is a very suitable means for preserving antigens that lose their immunoreactivity (1). Fresh tissue, after being obtained, is quick-frozen in a flask of liquid nitrogen for a few seconds depending on the size of the tissue. The rapid introduction of ultracold temperatures prevents soluble materials from degrading and reinforces the structural components, steadfastly holding them in place. This method of preservation does not specifically alter the tissue in any way other than to cause some labile or low-concentration solutes to degrade slightly or lyophilize. In performing assays on frozen specimens, there is always a bit of denaturation as the sections are being prepared, because the cut section thaws in order to adhere to the glass slide. There is also the risk of lyophilization of important components as well as the threat of freeze/thaw conditions occurring in the freezer after the specimens are preserved. However, this method of producing frozen specimens for analysis by antibody is the closest one can come to in vivo conditions, as no chemical changes have been forced on the tissue. Instead, the tissue is bathed in the cold liquid form of the gas until frozen.