The paper is concerned with a study into the mechanisms of renal interstitial lesions of the secondary character seen in patients afflicted with chronic glomerulonephritis. 120 patients with mesangioproliferative and membranous proliferative glomerulonephritis were examined. The patients were distributed into groups depending on the disease acuity, the degree of glomerular sclerosis and the disease stage. Three major mechanisms of the augmentation of changes in the renal interstice have been revealed: 1) exacerbation of the underlying process; 2) the degree of fibroplastic and sclerotic lesions in the glomerulus; 3) drug sensitization.