Morphological changes (histopathological and ultra- structural lesions) have been described in Peking ducks with a generalized amyloidosis ((3-fibrylosis). Long and thin fibers of amyloid of diameter of 8-12 nm and a length of 1510-1580 nm localized extracellulary formed parallel structures or felt-like structures. Biosynthesis of amyloid probably resulted due to disturbances in the immune system of the bird. This view is supported by charges in electropherograms of serum proteins of the ducks.