DMSO was therapeutically administered to patients with FAP and in about half of the patients there was some clinical improvement. Urinary proteins were analyzed biochemically and immunochemically before and after DMSO administration in seven cases of amyloidosis. As the results, increased excretion of various proteins of different molecular weights in the urine was observed depending on cases and examined organs. The in vitro effects of DMSO on amyloid proteins were examined. DMSO-degraded amyloid proteins showed void-volume materials and lower molecular weight components on Sephadex G column elution profiles as did guanidine-degraded amyloid protein. Among various denaturating or reducing agents, DMSO is the least potent in dissolving amyloid fibrils into prealbumin-related proteins.