Two cases of nephrotic syndrome during bucillamine treatment were encountered in 1989 in our hospital; both patients had suffered from rheumatoid arthritis for 2 years. They had received 200 mg bucillamine orally per day for 3-4 months before the onset of the nephrotic syndrome. Discontinuation of bucillamine led to complete remission of the nephrotic syndrome within 1 year. Bucillamine is a new therapeutic agent for rheumatoid arthritis developed in 1982 in Japan. Since 1985, 14 cases of nephrotic syndrome, including the two cases reported here have been reported. We review these cases and discuss the pathogenesis.