Abstract Sulfur amino acids, such as taurine, hypotaurine, and thiotaurine, were found in high quantities in tissues of marine symbiotic organisms (e.g., bivalves, tubeworms) living close to hydrothermal vent sites. Therefore, they are assumed to play a key role in the S-oxidizing base metabolism or sulfide detoxification. We propose here a specific, rapid, and original analytical procedure for the direct determination of sulfur amino acids at the level of a few parts per billion in biological samples, avoiding the classical low specific post-column ortho-phthaldialdehyde derivatization step required by non-ultraviolet-absorbing molecules. Indeed, by coupling liquid chromatography on a porous graphitic stationary phase under isocratic conditions (10 mM ammonium acetate buffer adjusted to pH 9.3) to tandem mass spectrometry (ionization process by pneumatically assisted electrospray in negative ion mode), it is possible to perform specific quantification of these metabolites in less than 10 min directly in biological matrices without any derivatization step or other tedious sample treatments. Thus, taurine, hypotaurine, and thiotaurine have been identified and assayed in several deep sea organisms, showing that the developed method is well suited for this kind of application.