Human amyloid from different organs in secondary and primary amyloidosis, and amyloid in multiple myeloma was investigated by means of the electron microscope. As experimentally induced amyloid of mouse it is made up of delicate fibers of circa 100 A thickness, ensheathed in some kind of a homogeneous ground substance. These fibers have nothing in common with reticular and collagenous fibers. Frequently the fibers are arranged in bundles, an observation which will certainly account for the phenomena of double-refringence in amyloid. As a result the fibrous composition of amyloid can be regarded as typical for human and animal amyloid in general.