Gas-chromatographic and mass-spectrometric analysis of human fecal samples was performed to identify the volatile compounds responsible for fecal odor. The compounds identified with fecal odor were the methyl sulfides methanethiol, dimethyl disulfide, and dimethyl trisulfide. Skatole and indole, the benzopyrrole volatiles believed to be responsible for fecal odor, in fact elaborated a napthalenelike "mothball" odor in the crystalline state as well as after purging from feces. A small amount of hydrogen sulfide gas was also identified in fecal samples. The components responsible for fecal odor are complex and may be influenced by dietary and endogenous contributions. However, the major components are methyl sulfide compounds rather than skatole and indole as is currently believed.