Yeast nucleic acid has been shown by Okamoto (1) to induce the formation of a potent hemolysin in cultures of Streptococcus pyogenes. As reported b y Okamoto, and confirmed in the present paper, the effect of nucleic acid is readily demonstrable since the hemolytic activity of filtrates or supernates of nucleic acid-broth cultures is at least 20 to 100 times greater than the activity of cultures prepared in broth to which no nucleic acid has been added. On blood agar containing yeast nucleic acid, the effect is manifest by the appearance of very large zones of beta hemolysis around the colonies.The nucleic acid effect has been investigated further in order to define the conditions necessary for producing the hemolysin on a large scale and in a manner which will facilitate its purification. In addition, although some of the properties of the nucleic acid-induced hemolysin have been described b y It6 (2), the relationship of this hemolysin to the better characterized streptococcal hemolysins, streptolysin O and streptolysin S, requires clarification. Finally, an opportunity is afforded of studying an almost unknown biological effect of nucleic acid. Methods, Materials, and TerminologyPreparation of Peptone-Infusion Broth.--Fresh beef hearts, freed of gross fat, were ground and then mixed well with tap water, 1 liter of water for each pound of ground heart. Mter being brought to 85°C. and infused at that temperature for 45 minutes, the mixture was filtered while hot, through paper. To each liter of infusion was added 10 gin. peptone (neopeptone Difco) and 5 gin. reagent sodium chloride. After the ingredients were completely dissolved by bringing to a boil, the pI-I was brought to 7.9, the medium was boiled 1 to 2 minutes, and then filtered immediately through paper. The medium was sterilized in the autoclave at 121°C. for 15 to 30 minutes. Immediately before inoculating, a freshly prepared solution of sodium thioglycollate was added to give a final concentration of 0.01 per cent.Culture Technique.--A 6 to 8 hour peptone-infusion broth culture of Streptococcus pyogenes, strain C203S, was distributed in 0.5 ce. amounts among a large number of sterile tubes, and then rapidly frozen solid in an alcohol-carbon dioxide freezing mixture. The tubes were stored in a dry-ice chest until needed. When required, a tube was thawed at room temperature, the contents diluted 10 times in sterile saline, and 0.1 cc. inoculated into each 10 cc. of