Studies of heterotrophically and autotrophically grown Thiobacillus novellas (A.T.C.C. 8093) showed several differences in cell structure. The envelope of the heterotrophically grown cell appeared as a homogeneous three-layered structure. The envelope of the autotrophically grown cell under the same fixing and staining procedure also appeared as a three-layered structure; however, differences were evident in the outermost layer of the two envelopes. Chemical analysis and specific staining procedures suggested that globules present in the heterotrophic cells were made up of polysaccharide.