A total of 70 and 38 patients with diabetes mellitus were investigated to compare the diagnostic significance of radio-isotope renography (RRG) with 131I-hippuran and a radioimmunoassay with beta 2-microglobulin (beta 2-MG) in renal involvement. The first method was shown to be less informative than the beta 2-MG test: at the 1st (prenephrotic) stage of diabetic nephroangiopathy the detectability of glomerular disturbances with the beta 2-MG test was a 2-fold higher and was still growing in the presence of proteinuria. In progressive stages (II and III) of diabetic nephroangiopathy the detectability of glomerular disturbances rose almost twice using both methods but a tendency to the use of the second one was preserved. Dysfunction of the proximal tubules of the kidney was noted only in the patients with progressive diabetic nephroangiography using both methods equally.