Nonamyloid green birefringence following Congo red staining.

It was noted recently in our laboratory that the Congo red-stained sections of a muscle and sural nerve biopsy specimen showed the typical green birefringence associated with amyloid, but no amyloid could be demonstrated with electron microscopy. A study involving three different dyes, two different procedures, and six different fixatives revealed that the technique utilized was the most important consideration. With the exception of Carnoy's mixture, the fixative was relatively unimportant and the false birefringence was closely related to excess dye retained in the tissue.