Assuming, that deterioration of renal function in the primary glomerulonephritis may also result from the destructive lesions to parenchymal tissue of the renal cortex (with simultaneous lesions to renal tubuli), the assessment of the urinary excretion of beta 2-microglobulin could be approached as an indicator of renal function in this situation. The study involved 85 patients with chronic glomerulonephritis treated with immunosuppressors++. In these subjects beta 2-microglobulin concentration per one unit of the urine (UB2M) together with fractional excretion of this globulin (FEB2M) was studied. Statistically significant differences in mean UB2M and FEB2M values have been noted between patients with remission and with the lack of the remission following therapy. Gradual increase in UB2M values as well as FEB2M values have been noted with deterioration of excretory renal function. The results have shown, that the assays of UB2M, and particularly FEB2M, is a sensitive marker of proximal renal tubuli function and indirectly of the processes which take place in extraglomerular renal cortex structures. It might be there fore of prognostic value.