In this work the bile acids and certain of their derivatives have been studied with regard to their bacteriostatic power and relative activities in removing the Gram-positive complex from yeast. No correlation between these properties was obtained. A simple relationship was apparent, however, between the bacteriostatic activities of the compounds and their ability to depress the surface tension of the metabolism medium. The limiting dilution at which the 'active' bile acids were bacteriostatic for Staphylococcus aureus corresponded to a depression of the surface tension of the medium by approximately 4.5 dynes. The relationship between bacteriostatic power and surface activity was only valid for this particular series of compounds of closely related molecular structure.