Five non-anesthetized dogs were intravenously infused with 4% pyrithione at a constant rate of 2 ml per minute for 5 min.During the course of treatment,experimental animals had salivation, nausea, vomiting, urination and defecation. In according with the accumulation of infused drug,the symptoms got worse and worse progressively. Finally, convulsion and respiratory failure appeared and death occured due to heart arrest. One hour after infusion and just before death, the concentration of pyrithione in the blood was 341? 180?g/ml and 657?158?g/ml respectively.The average accumulative lethal dose of pyrithione by intravenous infusion was 0.77?0.07 g/kg for dogs.