This paper describes pathological and clinical investigations of glomerular lesions in bucillamine-induced nephropathy by analyzing biopsy materials from 9 patients with rheumatoid arthritis (RA). There was no specific predisposition for nephrotic syndrome induced by bucillamine in clinical profiles related to age, onset, duration of disease, sex, activity and dose of bucillamine. In light-microscopic, electron-microscopic and immunofluorescent findings, the characteristic changes were similar to those of idiopathic membranous glomerulonephritis (MGN). After discontinuance of bucillamine, the nephrotic syndrome improved slowly with or without corticosteroid therapy. Results confirmed that the most common lesion of nephrotic syndrome associated with bucillamine therapy in RA is MGN. We recommend that corticosteroid therapy should be restricted to cases with severe proteinuria.