1. After a consideration of the physicochemical properties of detergents, it was deemed worth while to study some of their physiological effects. As nonpolar-polar electrolytes, the detergents are surface-active and as such cytolytics; but probably due to their dispersing and wetting properties, they are cytolytic in a fashion different from that of other cytolytics. The detergents tested were alkyl sulfonates, alkyl sulfosuccinates, and bile salts. 2. The cytolytic power has been tested in two ways, (1) with red cells by following the escape of hemoglobin, (2) with muscles by measuring the development of an injury potential. In both series of experiments the threshold concentrations of action have been determined. The effect on the potentials has proved to be, in general, reversible. 3. The hemolytic and the myolytic power run fairly parallel to the surface activity. 4. Dehydrocholate has been found to be lacking in nonpolar-polar properties. 5. The stellate cells (Kupffer cells) of the Ringer-perfused frog liver are unable to take up colloidal dyestuffs (trypan blue and soluble blue R), except after addition of a small amount of serum to the perfusing Ringer solution. Only under the latter conditions, the uptake of dye is increased by adding a detergent. This seems to be due to the combined action of the proteins and the detergents. 6. The effect of relatively high concentrations of detergent is disintegration of the stellate cells; viz., cytolysis. There are reasons to assume that small concentrations, which produce a threshold increase of the dyestuff uptake, raise the functional activity.