The sulphate of Mn, Cu and Zn, in small quantities, increased the dry weight of yeast produced. Excessive quantities of Mn, Cu and Zn salts were toxic, resulting in decreased growth or death of the cells. Cu stimulated cell division and resulted in cells of smaller size than in the controls. Mn, Cu, and Zn stimulated production of CO2, Cu being more effective than Mn or Zn. CO2 was produced in larger quantities under anaerobic fermentation than under aerobic conditions. Control cultures containing dextrose gave but slightly more CO2 than did the sucrose controls.