Results are presented of own studies of extracellular DNA (exDNA) in experiment of animals with transplanted ovarian cancer, after exposure to ionizing radiation, with benign prostatic hyperplasia, clinical studies in patients with chronic obstructive pulmonary disease and with acute disorders of cerebral circulation. The possibilities of exDNA determination for minimally invasive diagnostics in oncological diseases, formation of risk groups, monitoring of diseases, studying mechanisms of action and individual sensitivity to drug therapy are considered.