In this study we have investigated the role of oral dimethylsulfoxide (DMSO) therapy in 2 patients with primary amyloidosis (AL) and in 2 patients with secondary amyloidosis (AA) to long-standing rheumatoid arthritis. DMSO treatment produced no beneficial effects in the patients with idiopathic amyloidosis. Instead the patients with secondary amyloidosis experienced a subjective improvement, a decrease of inflammatory activity of the rheumatoid arthritis and an unequivocal improvement of renal function following 3-6 months of DMSO therapy. No serious side effects of DMSO were observed except for unpleasant breath odour. We conclude that a treatment with oral DMSO may prolong life of patients with secondary amyloidosis.