Background. Amyloid A amyloidosis is an obstinate disease complication in chronic inflammatory disease, and there are few effective therapies. The objective of this study was to investigate the effect of oral dimethyl sulfoxide (DMSO) on amyloid A amyloidosis. Methods. Fifteen secondary amyloid A amyloidosis patients (4 men, 11 women; age, 23-70 years) were treated with DMSO between 1995 and 2003. DMSO was administered orally in all patients at a dose of 3-20g/day. The clinical symptoms together with the renal and gastrointestinal functions were evaluated before and after treatment. Results. Among the 15 patients, amyloid A amyloidosis was a complication of rheumatoid arthritis (RA) in 10, of Crohn’s disease in 4, and of Adult Still’s disease in 1. Nine cases mainly involved the kidney, with renal dysfunction and proteinuria, five mainly involved the gastrointestinal tract, with protein-losing gastroenteropathy and intractable diarrhea, and one involved both gastrointestinal and renal amyloidosis. DMSO treatment was successful in 10 (66.7%) of the 15 patients (RA, 6/10; Crohn’s disease, 4/4; Adult Still’s disease, 0/1). Eight weeks of DMSO administration improved the renal function and proteinuria in five out of ten renal amyloidosis patients, but had no effect on those patients with severe and/or advanced renal dysfunction. With regard to gastrointestinal amyloidosis, gastrointestinal symptoms, including diarrhea and protein-losing gastroenteropathy, were improved in six patients. No serious side effects were encountered with the DMSO treatment. Conclusions. Oral administration of DMSO is an effective treatment for amyloid A amyloidosis, especially for gastrointestinal involvement and the early stage of renal dysfunction. Background. Amyloid A amyloidosis is an obstinate disease complication in chronic inflammatory disease, and there are few effective therapies. The objective of this study was to investigate the effect of oral dimethyl sulfoxide (DMSO) on amyloid A amyloidosis. Methods. Fifteen secondary amyloid A amyloidosis patients (4 men, 11 women; age, 23-70 years) were treated with DMSO between 1995 and 2003. DMSO was administered orally in all patients at a dose of 3-20 g / day. The clinical symptoms together with the renal and Among the 15 patients, amyloid A amyloidosis was a complication of rheumatoid arthritis (RA) in 10, of Crohn’s disease in 4, and of Adult Still’s disease in 1. Nine cases mainly involved the kidney, with renal dysfunction and proteinuria, five mainly involved the gastrointestinal tract, with protein-losing gastroenteropathy and intractable diarrhea, and one involved both gastrointestinal and renal DMSO treatment was successful in 10 (66.7%) of the 15 patients (RA, 6/10; Crohn’s disease, 4/4; Adult Still’s disease, 0/1). Eight weeks of DMSO administration improved the renal function and proteinuria in five out of ten renal amyloidosis patients, but had no effect on those patients with severe and / or advanced renal dysfunction. With regard to gastrointestinal amyloidosis, gastrointestinal symptoms, including diarrhea and protein-losing gastroenteropathy, were improved in six patients. No serious side effects were encountered with the DMSO treatment. Conclusions. Oral administration of DMSO is an effective treatment for amyloid A amyloidosis, especially for gastrointestinal involvement and the early stage of renal dysfunction.