1. The cumulative subcutaneous L.D.50 of allicin is 5 mg./kg. and its acute subcutaneous toxicity 50 mg./kg. 2. The intraperitoneal toxic dose of allicin at which 50% mortality occurred is 20 mg./kg. 3. The cumulative subcutaneous L.D.50 of pterygospermin is about 50 mg. and acute subcutaneous L.D.50 300 mg./kg. 4. Experiments show that pterygospermin like allicin is stable in presence of blood and gastric juice but unstable in presence of pancreatic juice. Experiments to find out the efficiency of pterygospermin, against bacterial infections of laboratory animals is in progress.