1. The sterile Berkefeld filtrates of broth cultures of certain strains of Staphylococcus aureus have a selective poisonous action for the skin of rabbits.

2. The poison is thermolabile, being completely destroyed when heated to 55°C for 1 hour.

3. The poison when injected intradermally into rabbits stimulates the production of antitoxin. We therefore conclude that the poison is a soluble toxin.