The LD₅₀ of rhomotoxin in mice was 0.522 mg/kg i.p. In dogs, its effective antihypertensive dose was 3.5µg/kg i.v. By 6 times the above dose, arrhythmias and changes of T wave occurred in most dogs, however, all these changes would disappear promptly and spontaneously. By 20 times the dose, death occurred in some dogs. By 30 times the dose, ventricular fibrillation occurred which resulted in death of all the animals. Rhomotoxin in effective antihypertensive dose decreased the contractility of the heart muscle slightly and temporarily, but it had no significant effect on respiration. Large dose (35 µg/kg) of rhomotoxin seemed to have no remarkable influence upon the functions of the liver and kidney in rabbits, nor did it do any significant damage to the heart, liver and kidney in pathological studies.