Following 689 percutaneous renal biopsies, membranous glomerulonephritis was proved in 68 patients. In 16 (23.5%) an underlying primary disease was verified, and thus the glomerulonephritis the secondary form. The primary disease was SLE in 5 cases, diabetes mellitus in 5 cases, rheumatoid arthritis in 3 cases, chronic active hepatitis in 2 cases, an ulcerative colitis and eosinophilic angiolymphoid hyperplasia in 1 patient. As initial sign, nephrotic syndrome emerged in 87.5% of the 16 cases. Microscopic haematuria was observed in half of the patients, as was hypertension, while acute renal failure presented in only 1 case. Histologically, in 13 cases the predominance of early glomerular alterations was characteristic, while in 9 cases the picture proved to be equivocal and accompanied by some degree of interstitial alterations. During combined treatment, remission was achieved in 75%. Two patients with SLE died, but not as a consequence of renal failure. Transient side-effects of the treatment were registered in 5 cases. The principal pathogenetic and clinical differences between the individual secondary nephritis forms, and the difficulty of their differentiation from the idiopathic cases, even on repeated examination, are emphasized. In 3 patients the possibility of secondary renal processes was suggested by the histological picture, and this was proved by the detailed clinical findings.