Staphylococcus aureus Smith was cultured in a synthetic tissue culture medium containing various concentrations of sodium chloride. The growth was at a higher level in the media containing sodium chloride of concentrations of 2.0 and 4.0% than in those of less than 2.0% and more than 4.0%. The result suggests that the bacteria grow more vigorously in the fairly high concentrations of sodium chloride than in the physiological concentration of it, in the synthetic medium. It may be considered that the high incidence of staphylococcal skin infections under hot conditions is due to the high level of growth of Staphylococcus aureus in fairly high concentrations of sodium chloride produced by hypersweating on the skin.