The solid content of several halophilic bacteria was estimated by immersion refractometry. Values for extreme halophiles ranged from 28 to 32%, and for moderate halophiles from 31 to 45%. The solid content of these organisms changed with variation in the salt content of the environment. It is thought that these differences are the result of changes in the water content of the cell. Spheres (spheroplasts) had a slightly lower solid content than the parent rods. Nuclear and other inclusion bodies, mostly of lower refractive index than the cytoplasm, were noted.