Congo red method for demonstrating amyloid in paraffin sections

A rapid, simple, and immunocytochemically compatible staining method for am yloid applicable to sections of human specimens embedded in paraffin is des cribed. Human necropsy material was fixed in buffered formalin, sectioned a t 5-10 mu m, mounted on slides, deparaffinized, and partially hydrated (70% ethanol). After partial hydration, sections were stained for amyloid for 1 0 min in a solution of 0.2% Congo red in 70% isopropanol. Sections were the n washed and counterstained for 10 min in a solution of 0.01% thionin, 0.01 % cresyl violet, 0.05% methyl green, 10% formaldehyde, and 0.5% acetic acid . After washing and dehydration, sections were cleared in eucalyptol and mo unted in Eukitt. Amyloid deposits appeared pink to red whereas cell nuclei and Nissl substance stained blue. This simple and consistent stain provides excellent nuclear staining that is useful for light microscopy observation and photography. With polarizing microscopy amyloid deposits show the char acteristic green dichroism. The present method can be used in combination w ith pre- or post-immunocytochemical techniques.