Experiments on Wistar male rats have shown that in 2 weeks the administration of streptozotocin results in an increase in relative kidney mass by 23%, the development of submicroscopic rearrangements indicating the hypertrophy of the main glomerular components and the acceleration of ultrafiltration. In one month a sharp widening of the lumens of capillaries and intersubosseous spaces, inflammatory symptoms, and signs of primary urine congestion are noted in parallel with hypertrophic changes. The relative kidney mass increases by 73.5% (p less than 0.01). The use of the aldose reductase blocker isodibut prevents, to a great extent, the development of ultrastructural changes in a glomerulus detected one month after administration of streptozotocin, improves ultrafiltration and inhibits a sharp increase in kidney mass, i. e. it prevents disorder of renal excretory function at the initial stages of experimental diabetes.