Vitreous amyloid may be the presenting clinical manifestation of types 1 and 2 familial amyloidotic polyneuropathy or complicate the course of these syndromes. Recent studies have shown that the major subunit protein composing amyloid fibrils in these conditions is a variant or abnormal prealbumin molecule and that affected individuals have low levels of this protein in their blood. The authors studied material obtained at vitrectomy from two cases of vitreous amyloid. One of these was nonfamilial and the other familial. Two-dimensional gels of solubilized protein from pelleted and washed vitreous amyloid in both cases were found to consist of material with the molecular weight and isofocusing coordinates of prealbumin monomer. Reactivity of fibrils with a monospecific antiserum to prealbumin was confirmed by colloidal gold immunoelectron microscopy. Non-familial as well as familial vitreous amyloid may in fact be systemic forms of amyloidosis due to deposition of prealbumin which can be characterized by biochemical or immunohistologic studies of material obtained at vitrectomy.