The toxin of the burned skin of rats purified by the immunochemical method possessed a definite physiological activity towards the cardiovascular system of homologous animals. The preparation introduced into the circulation caused in the course of 2 hours a reduction of the total arterial pressure from 125 +/- 7 mm Hg 74 +/- 8 mm Hg. Development of systemic hypotension was accompanied by secondary disturbance of microcirculation in the mesentery of the small intestine in the form of contraction, of arterioles, retarding the blood flow along the venules, and reduction of the capillary circulation.