• In ten previously undiagnosed patients, we have found erstwhile-"primary" nonhereditary amyloidosis as an overlooked cause of a predominately sensory, painful, and hyperesthetic distal neuropathy occurring in middle-aged and older patients. These symptoms, associated with orthostatic hypotension, diarrhea or constipation, cardiac abnormality, and male impotence are virtually diagnostic (in the absence of diabetes mellitus). Tissue diagnosis is quickly made by crystal-violet metachromasia of amyloid in fresh-frozen sections of a muscle biopsy specimen. Immunoglobulin and bone marrow evidence of plasma cell dyscrasia in eight of the ten patients suggests that the neuropathy in this form of amyloidosis is actually secondary to a plasma-cell-originating dysproteinemia. Therapy with melphalan and prednisone was not of benefit.