Surface-tension, light-scattering, and refractometric measurements were made on aqueous solutions of sodium taurodeoxycholate and sodium glycodeoxycholate in the presence of varying amounts of NaCl or NaI (0–0.5 M). Critical micellar concentrations (c.m.c), molecular areas, refractive index increments, micellar molecular weights and aggregation numbers, and effective charges per micelle were obtained. The two conjugated bile salts exhibited rather similar behavior. The micellar properties of bile salts were much like those of typical anionic detergents. The c.m.c. values were of the order of several millimoles per liter in water, and decreased with increasing concentration of electrolyte. Areas per molecule were in the vicinity of 90 Å2, closely corresponding to the area occupied by the steroid nucleus lying flat at the interface. Aggregation numbers varied from 8 in water to about 50 in 0.5 M electrolyte solutions.