The development of equipment and techniques that permit application of Sabatier's classical discoveries in vapor-phase hydrogenation to micro samples was accomplished just six years ago in our laboratories. Since then many improvements in the procedure have been made, and identifications of sulfur compounds in petroleum, previously thought impossible with the quantities of materials available, are now being made routinely. Many laboratories around the world are using the procedure and modifications thereof for structure determination of naturally occurring organic compounds. This technique rapidly and quantitatively removes the sulfur atom from organic sulfur compounds to produce paraffins or cycloparaffins. Identification of the produced hydrocarbon identifies or contributes to the identification of the precursor. The technique is direct, applicable to extremely small samples (5 × 10−6 ml), and requires no costly apparatus. The method also has been applied successfully to halogen-, oxygen-, and nitrogen-containing compounds. In addition it has been applied, with success, to the removal of other hetero atoms such as phosphorus, silicon, and metals. Only a few anomalies have been found, principally in the deoxygenation reaction. The basic technique, with recent improvements, permits structure characterization that would be difficult or impossible by any other procedure.