A simple and reproducible histochemical method for distinguishing different chemical types of amyloid is described. The method is based on the affinity of amyloid for Congo red dye after exposure to potassium permangenate and dilute sulfuric acid. The permanganate method represents a modification of the Romhanyi trypsin technique. It yields comparable results while obviating some of the technical difficulties associated with the latter method. The permanganate reaction was applied to a series of amyloid samples of known amino acid composition, to amyloid samples fixed in a variety of different preservatives, and to tissues obtained at autopsy from 67 amyloidosis patients whose disease had been previously subclassified on the basis of clinical presentation and autopsy observations. This method distinguished amyloid protein AA from other varieties of amyloid and proved effective when applied to amyloid samples preserved in any of several commonly used fixatives. This simple histochemical method proved useful in subclassifying amyloid type in the patient series particularly when used in conjunction with the available clinical history and the organ distribution of amyloid accumulation.