The invention relates to medicine and veterinary science and can be used for treating diseases associated with changes of the qualitative and/ quantitative composition of blood extracellular DNA, namely diseases provoked by atherosclerosis and pancreatic diabetes. The inventive method for treating the diseases consists in injecting an agent destroying blood extracellular DNA. DNAse enzyme injected into a systemic blood circulation in doses which modify the electrophoretic profile of the blood extracellular DNA definable by pulse-electrophoresis can be used in the form of an agent destroying said blood extracellular DNA. Said DNAse enzyme can be injected in doses and at regimes ensuring the level of a blood plasma DNA-hydrolytic activity which is measured in the blood plasma and is higher than 150 Kunitz units per litre of plasma during a total time higher than 12 hours a day.
